Which work measurement system involves observing employees randomly over an extended period of time?

Time Study

Time study is a structured process of directly observing and measuring human work using a timing device to establish the time required for completion of the work by a qualified worker when working at a defined level of performance.

It follows the basic procedure of systematic work measurement of:

• analysis of the work into small, easily-measurable components or elements
• measurement of those components and
• synthesis from those measured components to arrive at a time for the complete job.

The observer first undertakes preliminary observation of the work (a pilot study) to identify suitable elements which can be clearly recognised on subsequent occasions and are of convenient length for measurement.

Subsequent studies are taken during which the observer times each occurrence of each element using a stopwatch or other timing device while at the same time making an assessment of the worker's rate of working on an agreed rating scale. One of the prime reasons for measuring elements of work, rather than the work as a whole is to facilitate the process of rating. The rate at which a worker works will vary over time; if elements are carefully selected, the rate of working should be consistent for the relatively short duration of the element. More information on rating is given within the entry on work measurement. This assessment of rating is later used to convert the observed time for the element into a basic time; a process referred to as "extension". It is essential that a time study observer has been properly trained in the technique and especially in rating.

Time study, when properly undertaken, involves the use of specific control mechanisms to ensure that timing errors are within acceptable limits. Increasingly, timing is by electronic devices rather than by mechanical stopwatch; some of these devices also assist in subsequent stages of the study by carrying out the process of "extending" or converting observed times into basic times. The basic time is the time the element would take if performed at a specified standard rating.

The number of cycles that should be observed depends on the variability in the work and the level of accuracy required. Since time study is essentially a sampling technique in which the value of the time required for the job is based on the observed times for a sample of observations, it is possible using statistical techniques to estimate the number of observations required under specific conditions. This total number of observations should be taken over a range of conditions where these are variable and, where possible, on a range of workers.

Once a basic time for each element has been determined, allowances are added (for example, to allow the worker to recovere from the physical and mental effects of carrying out the work) to derive a standard time.

Time study is a very flexible technique, suitable for a wide range of work performed under a wide range of conditions, although it is difficult to time jobs with very short cycle times (of a few seconds). Because it is a direct observation technique, it takes account of specific and special conditions but it does rely on the use of the subjective process of rating. However, if properly carried out it produces consistent results and it is widely used. Additionally, the use of electronic data capture devices and personal computers for analysis makes it much more cost effective than previously.

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Introduction

Work measurement refer to the estimation of standard time, that is the time allowed for completing one piece of job using the given method. This is the time taken by an average experienced worker for the job with provisions for delays beyond the workers control.

There are several techniques used for estimation of standard time in industry. These include time study, work sampling, standard data, and predetermined time systems.

Definition:

Time study is a technique to estimate the time to be allowed to a qualified and well-trained worker working at a normal pace to complete a specified task.

This technique is based on measuring the work content of the task when performed by the prescribed method, with the allowance for fatigue and for personal and unavoidable delays.

Objectives and Applications:

Standard times for different operations in industry are useful for several applications like

• Estimating material machinery and equipment requirements.
• Estimating the production cost per unit as an input to
• Preparation of budgets
• Determination of selling price
• Make or buy decision
• Estimating manpower requirements.
• Estimating delivery schedules and planning the work.
• Balancing the work of operators working in a group.
• Estimating performance of workers and use as basis for incentive payment to those direct and in director labor who show greater productivity.

Time Study is the most versatile and the most widely used.

Time Study Equipment

The following equipment is needed for time study work

• Timing device
• Time study observation sheet
• Time study observation board
• Other equipment

Timing Device

The stop watch (Figure1) and the electronic timer are the most widely used timing devices used for time study. The two perform the same function with the difference that electronics timer can measure time to the second or third decimal of a second and can keep a large volume of time data in memory

Time Study Observation Sheet

It is a printed form with space provided for nothing down the necessary information about the operation being studied like name of operation, drawing number, name of the operator, name of time study person, and the date and place of study. Space are provided in the form for writing detailed description of the process (element-wise), recording stop-watch readings for each element of the process, performance rating(s) of the operator, and computation Figure 2 Shows a typical time study observation sheet.

Time Study Board

It is a light -weight board used for holding the observation sheet and stopwatch in position. It is of size slightly larger than that of observation sheet used. Generally, the watch is mounted at the center of the top edge or as shown in Figure 3 near the upper right-hand corner of the board. The board has a clamp to hold the observation sheet. During the time study, the board is held against the body and the upper left arm by the time study person in such a way that the watch could be operated by the thumb/index finger of the left hand. Watch readings are recorded on the observation sheet by the right hand.

Other Equipment

This includes pencil, eraser and device like tachometer for checking the speed, etc

Time Study Procedure:

The procedure for time study can best be described step-wise, which are self explanatory.

Step 1: Define objective of the study. This involves statement of the use of the result, the preci9sion desired, and the required level of confidence in the estimated time standards.

Step 2: Analyse the operation to determine whether standard method and conditions exist and whether the operator is properly trained. If need is felt for method study or further training of operator, the same may be completed before starting the time study.

Step 3: Select Operator to be studied if there is more than one operator doing the same task.

Step 4: Record information about the standard method, operation, operator, product, equipment, quality and conditions.

Step 5: Divide the operation into reasonably small elements.

Step 6: Time the operator for each of the elements. Record the data for a few number of cycles. Use the data to estimate the total numbers of observations to be taken.

Step 7: Collect and record the data of required number of cycles by timing and rating the operator.

Step 8: For each element calculate the representative watch time. Multiply it by the rating factory to get normal time.

Normal time = Observed time * Rating factor

Add the normal time of various elements to obtain the normal time for the whole operation.

Step 9: Determine allowances for various delays from the company's policy book or by conducting an independent study.

Step 10: Determine standard time by adding allowances to the normal time of operation.

Standard time = Normal time + allowances

Terms and Definition:

Normal Performance

There is no universal concept of Normal Performance. However, it is generally defined as the working rate of an average qualified worker working under capable supervision but not under any incentive wage payment scheme. This rate of working is characterized by the fairly steady exertion of reasonable effort, and can be maintained day after day without undue physical or mental fatigue.

The level of normal performance differs considerably from one company to another. What company A calls 100 percent performance, company B may call 80 percent, company C may call 125 percent and so on. It is important to understand that the level that a company selects for normal performance is not critical but maintaining that level uniform among time study person and constant with the passage of time within the company is extremely important.

There are, of course, some universally accepted benchmark examples of normal performance, like dealing 52 cards in four piles in 0.5 minute, and walking at 3 miles per hour (4.83 km/hr). In order to make use of these benchmarks, it is important that a complete description about these be fully understood, like in the case of card dealing, what is the distance of each pile with respect to the dealer, technique of grasping, moving and disposal of the cards.

Some companies make use of video films or motion pictures for establishing what they consider as normal speed or normal rate of movement of body members. Such films are made of typical factory jobs with the operator working at the desired normal pace. These films are reported to be useful in demonstrating the level of performance expected from the operators and also for training of time study staff.

Performance Rating

During the time study, time study engineer carefully observes the performance of the operator. This performance seldom conforms to the exact definition of normal or standard. Therefore, it becomes necessary to apply some 'adjustment' to the mean observed time to arrive at the time that the normal operator would have needed to do that job when working at an average pace. This 'adjustment' is called Performance Rating.

Determination of performance rating is an important step in the work measurement procedures. It is based entirely on the experience, training, and judgment of the work-study engineer. It is the step most subjective and therefore is subject to criticism.

It is the procedure in which the time study engineer compares the performance of operator(s) under observation to the Normal Performance and determines a factor called Rating Factor

System of Rating

There are several systems of rating, the performance of operator on the job. These are

1. Pace Rating
2. Westing house System of Rating
3. Objective Rating
4. Synthetic Rating

A brief description of each rating method follows

Pace Rating

Under this system, performance is evaluated by considering the rate of accomplishment of the work per unit time. The study person measures the effectiveness of the operator against the concept of normal performance and then assigns a percentage to indicate the ratio of the observed performance to normal or standard performance.

In this method, which is also called the speed rating method, the time study person judges the operators speed of movements, i.e. the rate at which he is applying himself, or in other words "how fast" the operator the motions involved.

Westing house System of Rating

This method considers four factors in evaluating the performance of the operator : Skill, effort, conditions and Consistency.

Skill may be defined as proficiency at following a given method. It is demonstrated by co ordination of mind and hands. A person's skill in given operation increases with his experience on the job, because increased familiarity with work bring speed, smoothness of motions and freedom from hesitations.

The Westing house system lists six classes of skill as poor fair, average, good, excellent in aTable1. The time study person evaluates the skill displayed by the operator and puts it in one of the six classes. As equipment % value of each class of skill is provided in the table, the rating is translated into its equivalent percentage value, which ranges from +15 % (for super skill) to - 22 % (for poor skill).

In a similar fashion, the ratings for effort, conditions, and consistency are given usingTable2 for each of the factors. By algebraically combining the ratings with respect to each of the four factors, the final performance-rating factor is estimated.

Objective Rating

In this system, speed of movements and job difficulty are rated separately and the two estimates are combined into a single value. Rating of speed or pace is done as described earlier, and the rating of job difficulty is done by selecting adjustment factors corresponding to characteristics of operation with respect to (i) amount of body used, (ii) foot pedals, (iii) bimanual ness, (iv) eye-hand co ordination, (v) handling requirements and (vi) weight handled or resistance encountered Mundel and Danner have given Table3 of % values (adjustment factor) for the effects of various difficulties in the operation performed.

For an operation under study, the numerical value for each of the six factors is assigned, and the algebraic sum of the numerical values called job difficulty adjustment factor is estimated.

The rating factor R can be expressed as

R = P x D

Where : P = Pace rating factor

             D = Job difficulty adjustment factor.

Synthetic Rating

This method of rating has two main advantages over other methods that (i) it does not rely on the judgment of the time study person and (ii) it give consistent results.

The time study is made as usual. Some manually controlled elements of the work cycle are selected. Using a PMT system (Pre- determined motion time system), the times for these elements are determined. The times of these elements are the performance factor is determined for each of the selected elements.

Performance or Rating Factor, R = P / A

Where P = Predetermined motion time of the element , A = Average actual Observed time of the element.

The overall rating factor is the mean of rating factors determined for the selected elements, which is applied uniformly to all the manually controlled elements of the work cycle.

Example

A work cycle has been divided into 8 elements and time study has been conducted. The average observed times for the elements are as :

M = Manually Controlled , P = Power Controlled

Total observed time of work cycle = 2.32 min.

Suppose we select elements number 2,5 and 8 (These must be manual y controlled elements). By using some PMT system, suppose we determine the times of these elements as

The mean of the rating factors of selected elements = 94.93 % or say95 % is the rating factor that will be used for all the manual elements of the work cycle.

The normal time of the cycle is calculated as given in the following table.

Normal Cycle Time

= 0.95(0.14+0.16+0.52+0.26+0.45+0.34+0.15)+1.00(0.30)

=1.92+0.30

=2.22 minutes

Standard Data Procedure:

In this procedure, we estimate the allowance for arriving the standard data.

Allowances

The readings of any time study are taken over a relatively short period of time. The normal time arrived at, therefore does not include unavoidable delay and other legitimate lost time, for example, in waiting for materials, tools or equipment; periodic inspection of parts; interruptions due to legitimate personal need, etc. It is necessary and important that the time study person applies some adjustment, or allowances to compensate for such losses, so that fair time standard is established for the given job.

Allowances are generally applied to total cycle time as some percentage of it, but sometimes these are given separately as some % for machine time and some other % for manual effort time. However no allowance are given for interruptions which maybe due to factor which are within the operator's control or which are avoidable.

Most companies allow the following allowances to their employees.

• Delay Allowance
• Fatigue Allowance
• Personal Allowance
• Special Allowance

Delay Allowance

This time allowance is given to an operator for the numerous interruptions that he experiences every day during the course of his work. These interruptions include interruptions from the supervisor, inspector, planners, expediters, fellow workers, production personnel and others. This allowance also covers interruptions due to material irregularities, difficulty in maintaining specifications and tolerances, and interference delays where the operator has to attend to more than one machine.

Fatigue Allowance

This allowance can be divided into two parts: (i) basic fatigue allowance and (ii) variable fatigue allowance. The basic fatigue allowance is given to the operator to compensate for the energy expended for carrying out the work and to alleviate monotony. For an operator who is doing light work while seated, under good working conditions and under normal demands on the sensory or motor system, a 4% of normal time is considered adequate. This can be treated as a constant allowance.

The magnitude of variable fatigue allowance given to the operator depends upon the severity of the factor or conditions, which cause extra (more than normal) fatigue to him. As we know, fatigue is not homogeneous, it range from strictly physical to purely psychological and includes combinations of the two. on some people it has a marked effect while on others, it has apparently little or no effect. Whatever may be the kind of fatigue-physical or mental, the result is same-it reduces the work output of operator. The major factors that cause more than just the basic fatigue includes sever working conditions, especially with respect to noise, illumination, heat and humidity; the nature of work, especially with respect to posture, muscular exertion and tediousness and like that.

It is true that in modern industry, heavy manual work, and thus muscular fatigue is reducing day by day but mechanization is promoting other fatigue components like monotony and mental stress. Because fatigue in totality cannot be eliminated, proper allowance has to be given for adverse working conditions and repetitiveness of the work.

Personal Allowance

This is allowed to compensate for the time spent by worker in meeting the physical needs. A normal person requires a periodic break in the production routine. The amount of personal time required by operator varies with the individual more than with the kind of work, though it is seen that workers need more personal time when the work is heavy and done under unfavorable conditions.

The amount of this allowance can be determined by making all-day time study or work sampling. Mostly, a 5 % allowance for personal time (nearly 24 minutes in 8 hours) is considered appropriate.

Special Allowance

These allowances are given under certain special circumstances. Some of allowances and the conditions under which they are given are:

Small Lot Allowance: This allowance is given when the actual production period is too short to allow the worker to come out of the initial learning period. When an operator completes several small-lot jobs on different setups during the day, an allowance as high as 15 percent may be given to allow the operator to make normal earnings.

Training Allowance: This allowance is provided when work is done by trainee to allow him to maker reasonable earnings. It may be a sliding allowance, which progressively decreases to zero over certain length of time. If the effect of learning on the job is known, the rate of decrease of the training allowance can be set accordingly.

Rework Allowance: This allowance is provided on certain operation when it is known that some present of parts made are spoiled due to factors beyond the operator's control. The time in which these spoiled parts may be reworked is converted into allowance.

Different organizations have decided upon the amount of allowances to be given to different operators by taking help from the specialists / consultants in the field and through negotiations between the management and the trade unions. ILO has given its recommendations about the magnitude of various allowances, Table 4.

Example:

In making a time study of a laboratory technician performing an analysis of processed food in a canning factory, the following times were noted for a particular operation.

If the technician's performance has been rated at 120 percent, and the company policy for allowance (personal, fatigue, etc.) stipulates 13 percent.

1. Determine the normal time.
2. Determine the standard time.

Watch readings falling 50 % above and 25 % below the average may be considered as abnormal.

Ans :

Work Sampling:

Work Sampling (also sometimes called ratio delay study) is a technique of getting facts about utilization of machines or human beings through a large number of instantaneous observations taken at random time intervals. The ratio of observations of a given activity to the total observations approximates the percentage of time that the process is in that state of activity. For example, if 500 instantaneous observations taken at random intervals over a few weeks show that a lathe operator was doing productive work in 365 observations and in the remaining 135 observations he was found 'idle' for miscellaneous reasons, then it can be taken that the operator remains idle (135/500) x 100 = 27 % 0f the time. Obviously, the accuracy of the result depends on the number of observations. However, in most applications there is usually a limit beyond which greater accuracy of data is not economically worthwhile

Use of Work Sampling for Standard Time Determination

Work sampling can be very useful for establishing time standards on both direct and indirect labor jobs. The procedure for conducting work sampling study for determining standard time of a job can be described step-wise.

Sampling Procedure:

Step 1. Define the problem. (i) Describe the job for which the standard time is to be determined. (ii) Unambiguously State and discriminate between the two classes of activities of operator on the job: what are the activities of job with which if operator is found engaged would entitle him to be in 'working" state. This would imply that when operator will be found engaged in any activity other than those would entitle him to be in "Not Working" state.

Step 2. Design the Sampling plan. (i) Estimate satisfactory number of observations to be made. (ii) Decide on the period of study, e.g. two days, one week, etc. (iii) Prepare detailed plan for taking the observations. This will include observation schedule, exact method of observing, design of observation sheet route to be followed, the particular person to be observed at the observation time, etc.

Step 3. Contact the person concerned and take them in confidence regarding conduct of the study.

Step 4. Collect the data at the pre-decided random times.

We will now briefly discuss some important issues involved in the procedure.

Number of Observations

As we know, result of study based on larger number of observations are more accurate, but taking more and more observation consume time and thus is costly. A cost-benefit trade-off has thus to be struck. In practice, the following methods are used for estimation of the number of observation to be made.

(i) Based on judgment. The study person can decide the necessary number of observations based on his judgment. The correctness of the number may be in doubt but estimate is often quick and adequate in many cases.

(ii) Using cumulative plot of results. As the study progresses the results (of the proportion of time devoted to the given activity, i.e. Pi from the cumulative number of observations are plotted at the end of each shift or day. A typical plot is shown in Figure4. Since the accuracy of the result improves with increasing number of observation, the study can be continued until the cumulative Pi appears to stabilize and collection of further data seems to have negligible effect on the value of Pi.

(iii) Use of statistics. In this method, by considering the important of the decision to be based on the results of study, a maximum tolerable sampling error in terms of confidence level and desired accuracy in the results is specified. A pilot study is then made in which a few observations are taken to obtain a preliminary estimate of Pi. The number of observations N necessary are then calculated using the following expression.

Where S = desired relative accuracy

Pi = estimate of proportion of time devoted to activity expressed as a decimal,

e.g. 5 % = 0.05

χ = a factor depending on the confidence level.

χ = 1, 2, 3 for confidence levels of 68 %, 95 % and 99 % respectively.

N = total number of observations needed.

The number of observations estimated from the above relation using a value of Pi obtained from a preliminary study would be only a first estimate. In actual practice, as the work sampling study proceeds, say at the end of each day, a new calculation should be made by using increasingly reliable value of Pi obtained from the cumulative number of observations made.

Determination of Observation Schedule

The number of instantaneous observations to be made each day mainly depends upon nature of operation. For example, for non-repetitive operations or for operations in which some elements occur in frequently, it is advisable to take observations more frequently so that the chance of obtaining all the facts improves. It also depends on the availability of time with the person making the study. In general, about 50 observations per day is a good figure. The exact (random) schedule of the observations is prepared by using random number table or any other technique.

Design of Observation Sheet

A sample observation sheet for recording the data with respect to whether at the pre-decided time, the worker on job is in 'working' state or 'non-working' state is shown in figure5. It contains the relevant information about the job, the operators on job, etc. At the end of each day, calculation can be done on the percent of time workers on the job (on an average) spend on activities, which are considered as part of the work method

Standard Time Determination

In this method of work measurement, the observed time for a given job is estimated as the working time divided by the number of units produced during that time.

Where T = Total study period

N = Number of units produced in study period

ηi =Number of observations in which worker(s) was found in 'working' state

ηi =Number of observations in which worker(s) was found in 'working' state

The normal time (NT) is found by multiplying the observed time by the average performing index (rating factor).

Where= Average rating factor =

Finally, the standard time is found by adding allowances to the normal time.

Example

A work sampling study was made of a cargo loading operation for the purpose of developing its standard time. The study was conducted for duration of minutes during which 3000, 1500 instantaneous observations were made at random intervals. The results of study indicated that the worker on the job was working 80 percent of the time and loaded 360 pieces of cargo during the study period. The work analyst rated the performance at 90 %. If the management wishes to permit a 13 % allowance for fatigue, delays and personal time, what is the standard time of this operation?

Ans:

Here, Total period = 1500 minutes

Working fraction = 80 percent

Average rating = 90 percent

Number of units loaded = 360

Allowances = 13 %

Advantages and Disadvantages of Work Sampling in Comparison with Time Study.

Advantage

Economical

1. Many operators or activities are difficult or uneconomical to measure by time study can readily be measured by work sampling
2. Two or more studies can be simultaneously made of several operators or machines by a single observer. Ordinarily a work study engineer can study only one operator at a time when continuous time study is made
3. It usually requires fewer man-hours to make a work sampling study than to make a continuous time study. The cost may also be about a third of the cost of a continuous time study
4. No stopwatch or other time measuring device is needed for work sampling studies.
5. It usually requires less time to calculate the results of work sampling study. Mark sensing cards may be used which can be fed directly to the computing machines to obtain the results just instantaneously. Flexible

Flexible

6. A work sampling study may be interrupted at any time without affecting the results.
7. Operators are not closely watched for long period of time. This decreases the chance of getting erroneous results for when a worker is observed continuously for a long period, it is probable that he will not follow his usual routine exactly during that period.

Less Erroneous

8. Observations may be taken over a period of days or weeks. This decreases the chance of day-to-day or week-to-week variations that may affect the results.

Operators Like It

9. Work sampling studies are preferred to continuous time study by the operators being studied. Some people do not like to be observed continuously for long periods of time.

Observers Like It

10. Work sampling studies are less fatiguing and less tedious to make on the part of time study engineer.  

Applications

11. Work sampling is applicable to a wide variety of situations in manufacturing, distribution, or service industries.

12. Work sampling is useful when determine the nature of the distribution of work activities within a gang operation.  

Disadvantage

1. Work sampling is not economical for the study of a single operator or operation or machine. Also, work-sampling study may be uneconomical for studying operators or machines located over wide areas.  
2. Work sampling study does not provide elemental time data.
3. The operator may change his work pattern when he sees the observer. For instance, he may try to look productive and make the results of study erroneous.
4. No record is usually made of the method being used by the operator Therefore a new study has to be made when a method change occurs in any element of operation.
5. Compared to stop watch time study, the statistical approach of work sampling study is difficult to understand by workers.

Computerized Work Sampling

Use of a computer can save as much as 30 to 40 percent of the total work sampling study cost. This is because too much clerical effort is involved in summarizing work sampling data, e.g. in determining the number of observations required, determining the daily observations required, determining the number of trips to the area being studied per day, determining the time of each observation, calculating the accuracy of results, plotting data on control charts and like that. Computers can be made use for mechanization of the repetitive calculations, display of control charts and calculation of daily as well as cumulative results.

Predetermined Motion Time System

A predetermined motion time system (PMTS) may be defined as a procedure that analyzes any manual activity in terms of basic or fundamental motions required to performing it. Each of these motions is assigned a previously established standard time value in such a way that the timings for the individual motions can be synthesized to obtain the total time for the performance of the activity.

The main use of PMTS lies in the estimation of time for the performance of a task before it is performed. The procedure is particularly useful to some organizations because it does not require troublesome rating with each study.

Applications of PMTS are for

1. Determination of job time standards.
2. Comparing the times for alternative proposed methods so as to find the economics of the proposals prior to production run.

3. Estimation of manpower, equipment and space requirements prior to setting up the facilities and start of production.

4. Developing tentative work layouts for assembly line prior to their working.

5. Checking direct time study results.

A number of PMTS are in use, some of which have been developed by individual organizations for their own use, while other organizations have publicized for universal applications.

The following are commonly used PMT systems

• Work factor (1938)  
• Method Time Measurement (1948)  
• Basic Motion Time (1951)  
• Dimension Motion Time (1954)  

Some important factors which be considered while selecting a PMT system for application to particular industry are

1. Cost of Installation. This consists mainly of the cost of getting expert for applying the system under consideration.
2. Application Cost. This is determined by the length of time needed to set a time standard by the system under consideration
3. Performance Level of the System. The level of performance embodied in the system under consideration may be different from the normal performance established in the industry where the system is to be used. However, this problem can be overcome by 'calibration' which is nothing but multiplying the times given in the Tables by some constant or by the application of an adjustment allowance.
4. Consistency of Standards. Consistency of standards set by a system on various jobs is a vital factor to consider. For this, the system can be applied on a trial basis on a set of operations in the plant and examined for consistency among them.
5. Nature of Operation. Best results are likely to be achieved if the type and nature of operations in the plant are similar to the nature and type of operations studied during the development of the system under consideration.

Advantages and limitations of using PMT systems

Advantage

Compared to other work measurement techniques, all PMT system claim the following advantages:

1. There is no need to actually observe the operation running. This means the estimation of time to perform a job can be made from the drawings even before the job is actually done. This feature is very useful in production planning, forecasting, equipment selection etc.
2. The use of PMT eliminates the need of troublesome and controversial performance rating. For the sole reason of avoiding performance rating, some companies have been using this technique.
3. The use of PM times forces the analyst to study the method in detail. This sometimes helps to further improve the method
4. A bye-product of the use of PM time is a detailed record of the method of operation. This is advantageous for installation of method, for instructional purposes, and for detection and verification of any change that might occur in the method in future.
5. The PM times can be useful y employed to establish elemental standard data for setting time standards on jobs done on various types of machines and equipment.
6. The basic times determined with the use of PMT system are relatively more consistent.

Limitations

There are two main limitations to the use of PMT system for establishing time standards. These are : (i) its application to only manual contents of job and (ii) the need of trained personnel. Although PMT system eliminates the use of rating, quite a bit of judgment is still necessarily exercised at different stages.