Work measurement professionals have to focus on machine time estimation also. Also, they have to focus on developing productivity science based on measurements that they are taking. My comment in work measurement Linkedin group.
The term "work measurement", is a term used to describe a family of techniques, any one of which can be used to measure work.
Work measurement is concerned with investigating, reducing and subsequently eliminating ineffective time, that is time during which no effective work is being performed, whatever the cause.
Work measurement, as the name suggests, provides management with a means of measuring the time taken in the performance of an operation or series of operations in such a way that ineffective time is shown up and can be separated from effective time. In this way its existence, nature and extent become known where previously they were concealed within the total.
One of the surprising things about plants where work measurement or any other waste elimination has not need been employed is the amount of ineffective time whose very existence is unsuspected — or which is accepted as "the usual thing" and something inevitable that no one can do much about — that is built into the process. Once the existence of ineffective time has been revealed and the reasons for it tracked down, steps can usually be taken to reduce it.
The above explanation of work measurement does not get emphasis in practice.
Taylor's Time Study as it is popularly known is used for identifying the best way doing different elements of an job. It is more appropriate to term it "Process Time Reduction Study."
(F.W. Taylor's Time Study - 1912 - Taylor's Process Time Reduction Study
https://nraoiekc.blogspot.com/2019/09/fw-taylor-explanation-of-time-study-1912.html
Time Study - 1903 Explanation by F.W. Taylor - Process Time Reduction Study
https://nraoiekc.blogspot.com/2013/08/time-study-by-fw-taylor.html)
Work measurement has another role to play. It can be used to set standard times for carrying out the work, so that, if any ineffective time does creep in later, it will immediately be shown up as an excess over the standard time and will thus be brought to the attention of management.
This role of work measurement to set standard time got all the emphasis in book by Barnes and also in the ILO Book. Readers have to note the shortcoming.
Method study reveals shortcomings of design, material, equipment, its accessories, cutting tools and method of manufacture, and, as such, affects mainly technical decisions. Work measurement is more likely to show up short comings on the part of management and the motions, movements and idle time of the workers.
On the basis of work measurement, the elimination of ineffective time due to management shortcomings must precede any attack on the ineffective time within the control of the workers.
Utility - Uses of work measurement:
(1) To compare the efficiency of alternative methods. Other conditions being equal, the method which takes the least time will be the best method.
(2) To balance the work of members of teams, in association with multiple activity charts, so that, as nearly as possible, each member has a task taking an equal time to perform (gang process chart) .
(3) To determine, in association with worker and machine multiple activity charts, the number of machines an operative can run .
The time standards, once set, may then be used:
(4) To provide the basis for production planning and control for the choice of a better layout and for process planning, and for establishing just-in-time inventory control systems .
(5) To provide information that can enable estimates to be made for tenders, selling prices and delivery dates.
(6)
To set standards of machine utilization and labour performance which can be used for any of the above purposes and as a basis for incentive schemes.
To use as basis for incentive schemes, the appropriate definition of work measurement is, "Work measurement is the application of techniques designed to establish the time for a qualified worker to carry out a task at a defined rate of working."
(7) To provide information for labour-cost control and to enable standard costs to be fixed and maintained.
The basic procedure
SELECT the work to be studied.
RECORD all the relevant data relating to the circumstances in which the work is being done, the methods and the elements of activity in them.
EXAMINE the recorded data and the detailed breakdown critically to ensure that the most effective method and motions are being used and that unproductive and foreign elements are separated from productive elements.
MEASURE the quantity of work involved in each element, in terms of time, using the appropriate work measurement technique.
COMPILE the standard time for the operation, which in the case of stop-watch time study will include time allowances to cover relaxation, personal needs, etc.
DEFINE precisely the series of activities and method of operation for which the time has been compiled and issue the time as standard for the activities and methods specified.
The techniques of work measurement
Principal techniques
- time study;
- structured estimating;
- standard data.
- predetermined time standards (PTS);
- work sampling;
CHAPTER 21 Time study: Selecting and timing the job
1. Selecting the job
Some possible reasons for ding a time study are:
(1) The job is a new one (new product, component, operation or set of activities).
(2) A change in material or method of working has been made and a new time standard is required.
(3) A complaint has been received about the time standard for an operation.
(4) A particular operation appears to be a "bottleneck" holding up subsequent operations.
(5) Standard times are required before an incentive scheme is introduced.
(6) The output of an equipment is low, and it therefore becomes necessary to investigate the method of its use.
(7)
The job needs studying as a preliminary to making a method study, or to compare the efficiency of two proposed methods.
(8) The cost of a particular job appears to be excessive.
If the purpose of the study is the setting of performance standards, it should not normally be undertaken until method study has been used to establish and define the most satisfactory way of doing the job.
A distinction is made in time study practice between what are termed representative workers and qualified workers. A representative worker is one whose skill and performance is the average of the group under consideration, and who is not necessarily a qualified worker. The concept of the qualified worker is an important one in time study. This person is defined as follows:
"A qualified worker is one who has acquired the skill, knowledge and other attributes to carry out the work in hand to
satisfactory standards of quantity, quality and safety."
If a new method has been installed, the worker must be allowed plenty of time to settle down before timing starts. It takes quite a long time for an operative to adapt and to reach a maximum steady speed. Depending on the duration and intricacy of the operation, it may be necessary to allow a job to
run for days or even weeks before it is ready to be timed for the purpose of setting standards. In the same way, the work done by new operatives should never be used for timing until they have grown thoroughly accustomed to their jobs.
The study person's exact position will be determined by the type of operation being studied, but the position generally recommended is to one side of the operative,
slightly to the rear and about 2 metres away.
The study board and watch should be held well up in line with the job, to make reading the watch and recording easy while maintaining continuous observation.
On no account should any attempt be made to time the operative without his or her knowledge, from a concealed position or with the watch in the pocket. It is dishonest and, in any case, someone is sure to see and the news will spread like wildfire. Work study should have nothing to hide.
Time study demands intense concentration and alertness, especially when timing very short "elements" or "cycles" (defined later in this chapter), and it is generally agreed that this is better attained when standing.
Steps in making a time study
When the work to be measured has been selected, the making of a time study usually consists of the following eight steps:
(1) Obtaining and recording all the information available about the job, the operative and the surrounding conditions, which is likely to affect the carrying out of the work.
(2) Recording a complete description of the method, breaking down the operation into "elements".
(3) Examining the detailed breakdown to ensure that the most effective method and motions are being used, and determining the sample size.
(4) Measuring with a timing device (usually a stop-watch) and recording the time taken by the operative to perform each "element" of the operation.
(5) At the same time, assessing the effective speed of working of the operative relative to the observer's concept of the rate corresponding to standard rating.
(6) Extending the observed times to "basic times".
(7) Determining the allowances to be made over and above the basic time for the operation.
(8) Determining the "standard time" for the operation.
Checking the Method
Before proceeding with the study, it is important to check the method being used by the operative. If the study is for the purpose of setting a time standard, a method study should already have been made and a written standard practice sheet completed. In this case it is simply a question of comparing what is actually being done with what is specified on the sheet. If the study is being made as the result of a complaint from workers that they are unable to attain the output set by a previous study, their methods must be very carefully compared with that used when the original study was made. It will often be found in such cases that the operatives are not carrying out the work as originally specified: they may be using different tools, a different machine setup or different speeds and feeds, temperatures, rates of flow or whatever the requirements of the process may be, or additional work may have crept in. It may be that the cutting tools are worn, or have been sharpened to incorrect profiles. Times obtained when observing work carried out with worn tools or incorrect process conditions should not be used for the compilation of time standards.
In highly repetitive short cycle work, such as work on a conveyor band (light assembly, packing biscuits, sorting tiles), changes in method may be much more difficult to detect, since they may involve changes in the movements of the arms and hands of the operative ("motion patterns") which can be observed only with difficulty by the naked eye and require special apparatus to analyse.
Breaking the job into elements
An element is a distinct part of a specified job selected for convenience of observation, measurement and analysis
A work cycle is the sequence of elements which are required to perform a job or yield a unit of production. The sequence may sometimes include occasional elements
A work cycle starts at the beginning of the first element of the operation or activity and continues to the same point in a repetition of the operation or activity. That is the start of the second cycle.
A detailed breakdown into elements is necessary:
(1) To ensure that productive work (or effective time) is separated from unproductive activity (or ineffective time).
(2) To permit the rate of working to be assessed more accurately than would be possible if the assessment were made over a complete cycle. The operative may not work at the same pace throughout the cycle, and may tend to perform some elements more quickly than others.
(3) To enable the different types of element (see below) to be identified and distinguished, so that each may be accorded the treatment appropriate to its type.
(4) To enable elements involving a high degree of fatigue to be isolated and to make the allocation of fatigue allowances more accurate.
(5) To facilitate checking the method so that the subsequent omission or insertion of elements may be detected quickly. This may become necessary if at a future date the time standard for the job is queried.
(6) To enable a detailed work specification to be produced.
(7) To enable time values for frequently recurring elements, such as the operation of machine controls or loading and unloading work pieces from fixtures, to be extracted and used in the compilation of standard data.
Types of elements
Eight types of element are distinguished: repetitive, occasional, constant, variable, manual, machine, governing, and foreign elements.
A
repetitive element is an element which occurs in every work cycle of an operation.
Examples: the element of picking up a part prior to an assembly operation; the element of locating a workpiece in a holding device; putting aside a finished component or assembly.
An
occasional element is an element which does not occur in every work cycle of an operation but which may occur at regular or irregular intervals.
Examples: adjusting the tension, or machine setting; receiving instructions from the supervisor. The occasional element is useful work and a part of the job. It will be incorporated in the final standard time for the job.
A
constant element is an element for which the basic time remains constant whenever it is performed.
Examples: switch on machine; gauge diameter; screw on and tighten nut; insert a particular cutting tool into machine.
A
variable element is an element for which the basic time varies in relation to some characteristics of the product, equipment or process, e.g. dimensions, weight, quality, etc.
Examples: saw logs with handsaw (time varies with hardness and diameter); sweep floor (varies with area); push trolley of parts to next shop (varies with distance).
A
manual element is an element performed by a worker.
A
machine element is an element performed automatically by any process, physical, chemical or otherwise that, once started, cannot be influenced by a worker except to terminate it prematurely.
Examples: anneal tubes, fire tiles; form glass bottles; press car body shell
to shape; most actual cutting elements on machine tools.
A
governing element is an element occupying a longer time within a work cycle than that of any other element which is being performed concurrently.
Examples: turn diameter on a lathe, while gauging from time to time; boil kettle of water, while setting out teapot and cups; develop photographic negative, while agitating the solution occasionally.
A
foreign element is an element observed which does not form a part of the operation(s) being studied
Examples: in furniture manufacture, sanding the edge of a board before planing has been completed; degreasing a part that has still to be machined further.
It will be clear from the definitions given above that a repetitive element may also be a constant element, or a variable one. Similarly, a constant element may also be repetitive or occasional; an occasional element may be constant or variable, and so on, for the categories are not mutually exclusive.
Deciding on the elements
There are some general rules concerning the way in which a job should be broken down into elements. They include the following:
Elements should be easily identifiable, with definite beginnings and endings so that, once established, they can be repeatedly recognized. These beginnings and endings can often be recognized by a sound (e.g. the stopping of a machine, unlocking a catch of a jig, putting down a tool) or by a change of direction of hand or arm. They are known as the "break points" and should be clearly described on the study sheet. A break point is thus the instant at which one element in a work cycle ends and another begins.
Elements should be as short as can be conveniently timed by a trained observer. The smallest practical unit that can be timed with a stop-watch, is generally considered to be about 0.04 min. (2.4 sec). For less highly trained observers it may be 0.07 to 0.10 min. Very short elements should, if possible, be next to longer elements for accurate timing and recording. Long manual elements should be rated about every 0.33 min. (20 sec).
As far as possible, elements — particularly manual ones — should be chosen so that they represent naturally unified and recognizably distinct segments of the operation. For example, consider the action of reaching for a wrench, moving it to the work and positioning it to tighten a nut. It is possible to identify the actions of reaching, grasping, moving to the work piece, shifting the wrench in the hand to the position giving the best grip for turning it, and positioning. The worker will probably perform all these as one natural set of motions rather than as a series of independent acts. It is better to treat the group as a whole, defining the element as "get wrench" or "get and position wrench" and to time the whole set of motions which make up the group, than to select a break point at, say, the
instant the fingers first touch the wrench, which would result in the natural group of motions being divided between two elements.
Manual elements should be separated from machine elements. This may sometimes be difficult for short cycles. However, although manual and machine time may run concurrently it may be necessary to measure them separately to derive standard data. Machine time with automatic feeds or fixed speeds can be calculated and used as a check on the stop-watch data.
Hand time is normally completely within the control of the operative.
Constant elements should be separated from variable elements.
Elements which do not occur in every cycle (i.e. occasional and foreign elements) should be timed separately from those that do. The necessity for a fine breakdown of elements depends largely on the
type of manufacturing, the nature of the operation and the results desired.
Assembly operations in the light electrical and radio industries, for example, generally have short cycle operations with very short elements. The importance of the proper selection, definition and description of elements must again be emphasized. The amount of detail in the description will depend on a number of factors, for instance:
Small batch jobs which occur infrequently require less detailed element descriptions than long-running, high-output lines.
Movement from place to place generally requires less description than hand and arm movements.
Elements should be checked through a number of cycles and written down before timing begins.
CHAPTER 22
Time study: Rating
The procedures described in this chapter represent sound current practice. They will certainly provide the reader with a sound basic system which will be suitable for most general applications, and one which can later be refined if the particular nature of certain special operations requires a modification of the system, so as to rate something other than effective speed.
In one study it was noted that it was only after some 8,000 cycles of practice that the times taken by workers began to approach a constant figure — which was itself half the time they took when they first tried the operation. Thus time standards set on the basis of the rate of working of inexperienced workers could turn out to be quite badly wrong, if the job is one with a long learning period. Some jobs, of course, can be learned very quickly.
Rating is the assessment of the worker's rate of working relative to the observer's concept of the rate corresponding to standard pace
Standard performance is the rate of output which qualified workers will naturally achieve without over-exertion as an average over the working day or shift, provided that they know and adhere to the specified method and provided that they are motivated to apply themselves to their work. This performance is denoted as 100 on the standard rating and performance scales
The rate of working most generally accepted in the United Kingdom and the United States as corresponding to the standard rating is equivalent to the speed of motion of the limbs of a man of average physique walking without a load in a straight line on level ground at a speed of 4 miles an hour (6.4 kilometres per hour). This is a brisk, business-like rate of walking, which a man of the right physique and well accustomed to walking might be expected to maintain, provided that he took appropriate rest pauses every so often. This pace has been selected, as a result of long experience, as providing a suitable benchmark to correspond to a rate of working which would enable the average qualified worker who is prepared to apply himself to his task to earn a fair bonus by working at that rate, without there being any risk of imposing on him any undue strain that would affect his health, even over a long period of time. (As a matter of interest, a man walking at 4 miles an hour (6.4 km/hr.) appears to be moving with some purpose or destination in mind: he is not sauntering, but on the other hand he is not hurrying. People hurrying, to catch a train for instance, often walk at a considerably faster pace before breaking out into a trot or a run, but it is a pace which they would not wish to keep up for very long.)
It should be noted, however, that the "standard pace" applies to Europeans and North Americans working in temperate conditions; it may not be a proper pace to consider standard in other parts of the world. In general, however, given workers of proper physique, adequately nourished, fully trained and suitably motivated, there seems little evidence to suggest that different standards for rates of working are needed in different localities, though the periods of time over which workers may be expected to average the standard pace will vary very widely with the environmental conditions. At the very least, the standard rate as described above provides a theoretical datum line with which comparisons of performance in different parts of the world could be made in order to determine whether any adjustment may be necessary.
Another accepted example of working at the standard rate is dealing a pack of 52 playing cards in 0.375 minutes.
When time standards are used as a basis for payment by results, many union-management agreements stipulate that the time standards should be such that a representative or average qualified worker on incentive pay can earn 20-35 per cent above the time rate by achieving the standard performance. If these workers have no target to aim at and no incentive to make them desire a higher output, they will (apart from any time consciously wasted) tolerate the intrusion of small amounts of ineffective time, often seconds or fractions of seconds between and within elements of work. In this way they may easily reduce their performance over an hour or so to a level well below that of the standard performance. If, however, they are given enough incentive to make them want to increase their output, they will get rid of these small periods of ineffective time, and the gaps between their productive movements will narrow. This may also alter the pattern of their movements.
Judgement of walking pace is only used for training work study persons in the first stages; it bears very little resemblance to most of the jobs that have to be rated. It has been found better to use films or live demonstrations of industrial operations.
Confidence in the accuracy of one's rating can be acquired only through long experience and practice on many types of operation — and confidence is essential to a work study person.
The effective speed of the operation has to be rated. Ineffective movements are to be identified and removed. Judgement of effective speed can only be acquired through experience and knowledge of the operations being observed.
It is very easy for an inexperienced study person either to be fooled by a large number of rapid movements into believing that an operative is working at a high rate or to underestimate the rate of working of the skilled operative whose apparently slow movements are very economical of motion.
Should effort be rated, and if so, how? The problem arises as soon as it becomes necessary to study jobs other than very light work where little muscular effort is required. Effort is very difficult to rate. The result of exerting effort is usually only seen in the speed.
The amount of effort which has to be exerted and the difficulty encountered by the operative is a matter for the study person to judge in the light of experience with the type of job. For example, if an operative has to lift a heavy mould from the filling table, carry it across the working area and put it on the ground near the ladle, only experience will tell the observer whether the speed at which it is being done is normal, above normal or subnormal. Those who had never studied operations involving the carrying of heavy weights would have great difficulty in making an assessment the first time they saw such an operation.
Factors affecting the rate of working
Variations in actual times for a particular element may be due to factors outside or within the control of the worker. Those outside this control may be:
- variations in the quality or other characteristics of the material used, although they may be within the prescribed tolerance limits;
- changes in the operating efficiency of tools or equipment within their useful life;
- minor and unavoidable changes in methods or conditions of operation;
- variations in the mental attention necessary for the performance of certain of the elements;
- changes in climatic and other surrounding conditions such as light, temperature, etc.
These can generally be accounted for by taking a sufficient number of studies to ensure that a representative sample of times is obtained.
Factors within the operative's control may be:
- acceptable variations in the quality of the product;
- variations due to the individual's ability;
- variations due to the attitude of mind, especially the attitude to the organization for which he or she works.
The factors within the worker's control can affect the times of similarly described elements of work by affecting:
- the pattern of the worker's movements;
- the individual working pace;
- both, in varying proportions.
The study person must therefore have a clear idea of the pattern of movement which a qualified worker should follow, and of how this pattern may be varied to meet the range of conditions which that worker may encounter. Highly repetitive work likely to run for long periods should have been studied in detail through the use of refined method study techniques, and the worker should have been suitably trained in the patterns of movement appropriate to each element.
The optimum pace at which the worker will work depends on:
- the physical effort demanded by the work;
- the care required on the part of the worker;
- training and experience.
Greater physical effort will tend to slow up the pace. The ease with which the effort is made will also influence the pace. For example, an effort made in conditions where operatives cannot exert their strength in the most convenient way will be made much more slowly than one of the same magnitude in which they can exert their strength in a straightforward manner (for instance, pushing a car with one hand through the window on the steering-wheel, as opposed to pushing it from behind). Care must be taken to distinguish between slowing up due to effort and slowing up due to fatigue.
Scales of rating
There are several scales of rating in use, the most common of which are those designated the 60-80, 75-100 and 100-133 scales. The British Standard scale, 0-100 scale, is used in this book. It is essentially a restatement of the 75-100 scale.
In the 60-80, 75-100 and 100-133 scales, the lower figure in each instance was defined as the rate of working of an operative on time rates of pay; and the higher, in each case one-third higher, corresponded to the rate of working we have called the standard rate, that of qualified workers who are suitably motivated to apply themselves to their work, as for instance by an incentive scheme. The underlying assumption was that workers on incentive perform, on average, about one-third more effectively than those who are not. This assumption has been well substantiated by practical experience over many years, but it is largely irrelevant in the construction of a rating scale. All the scales are linear. There is therefore no need to denote an intermediate point between zero and the figure chosen to represent the standard rating as we have defined it. Whichever scale is used, the final time standards derived should be equivalent, for the work itself does not change even though different scales are used to assess the rate at which it is being carried out.
The newer 0-100 scale has, however, certain important advantages which have led to its adoption as the British Standard. It is commended to readers of this book and is used in all the examples which follow. In the 0-100 scale, 0 represents zero activity and 100 the normal rate of working of the motivated qualified worker— that is, the standard rate.
Recording the rating
In general, each element of activity must be rated during its performance before the time is recorded, without regard to previous or succeeding elements.
In the case of very short elements and cycles this may be difficult. If the work is repetitive, every cycle or possibly the complete study may be rated. This is done when the short cycle study form is used.
It is most important that the rating should be made while the element is in progress and that it should be noted before the time is taken, as otherwise there is a very great risk that previous times and ratings for the same element will influence the assessment. For this reason the "Rating" column on the time study sheet is placed to the left of the "Watch reading" column. It is, perhaps, a further advantage of the cumulative method of timing that the element time does not appear as a separate figure until the subtractions have been made later in the office. If it did, it might influence the rating or tempt the study person to "rate by the watch".
Since the rating of an element represents the assessment of the average rate of performance for that element, the longer the element the more difficult it is for the study person to adjust this judgement to that average. This is a strong argument in favour of making elements short. Long elements, though timed as a whole up to the break points, should be rated every half-minute.
Rating to the nearest five is found to give sufficient accuracy in the final result. Greater accuracy than this can be attained only after very long training and practice.
We have discussed the filling-in of two columns, namely "Watch reading" (WR) and "Rating" (R), both entries being made on the same line. These readings are continued for a sufficient number of cycles. The study is then at an end. The next step, after thanking the operative for his or her cooperation, is to work out the basic time for each element. How to do this is described in the next chapter.
Updated on 27.8.2021, 7 September 2020, 29 October 2019, 3 August 2019
