Time Study and Work Measurement in Operations Management

Work mea­sure­ment is the appli­ca­tion of tech­niques designed to estab­lish the time for a qual­i­fied worker to carry out a spec­i­fied job at a defined level of per­for­mance. Time study is its best-known tech­nique: an ana­lyst observes a job, breaks it into ele­ments, times each ele­ment over sev­eral cycles, adjusts for the work­er's pace and adds allowances to arrive at a stan­dard time.

With­out time stan­dards, man­age­ment works on guess­work. It can­not say how long a job should take, whether a slow result is due to the worker or the method, how many peo­ple a plan needs, or what a fair incen­tive tar­get is. With a mea­sured stan­dard, a super­vi­sor can say "this car­ton should take about 1.12 min­utes" instead of "do it quickly", and plan­ning, cost­ing and wage deci­sions rest on evi­dence.

Objec­tives and uses of work mea­sure­ment

The main objec­tive is to deter­mine the stan­dard time for a job under nor­mal con­di­tions. That sin­gle fig­ure answers sev­eral man­age­ment ques­tions: how long the job should take, how many work­ers are needed, how much out­put to expect and how to sched­ule the work.

Uses of stan­dard time

• pro­duc­tion plan­ning, sched­ul­ing and deliv­ery promises
• man­power plan­ning and capac­ity plan­ning
• line bal­anc­ing on assem­bly lines
• labour cost­ing, esti­mat­ing and pric­ing
• wage incen­tive schemes and fair out­put tar­gets
• com­par­ing the pro­duc­tiv­ity of work­ers, shifts and alter­na­tive meth­ods
• reveal­ing idle time, delays and under­used equip­ment

What goes wrong with­out it

Sched­ules become unre­li­able, labour plans inac­cu­rate, tar­gets unre­al­is­tic, incen­tives unfair, machine load­ing dif­fi­cult and cost esti­mates poor.

Work mea­sure­ment and time study com­pared

Work mea­sure­ment is the broad field; time study is one tech­nique inside it. The objec­tive of time study is to find the time an aver­age (qual­i­fied) worker needs under nor­mal con­di­tions, nei­ther an unusu­ally slow nor an unusu­ally fast one.

Because a time stan­dard is only as good as the method it mea­sures, method study should come first; time study then sets the time for the improved method.

Equip­ment for time study

• Stop­watch: tra­di­tion­ally a dec­i­mal-minute watch read­ing to 0.01 minute; today often a dig­i­tal timer or a tablet app.
• Time study board: a clip­board that holds the watch and the form so the ana­lyst can read and write together.
• Time study (obser­va­tion) sheet: a form list­ing the ele­ments down the side and the cycles across the top.
• Cal­cu­la­tor or com­puter for the analy­sis, and some­times a video cam­era for detailed or micro­mo­tion study.

Instru­ments unre­lated to tim­ing, such as a ther­mome­ter, are not part of time study equip­ment.

Steps in a stop­watch time study

1. Select the job and the worker

Choose a job where a stan­dard is needed: out­put is impor­tant, time is uncer­tain, delays are com­mon or cost is high. Choose a qual­i­fied, expe­ri­enced worker who works at a steady pace, and explain the pur­pose of the study to the worker and the super­vi­sor.

2. Record and stan­dard­ise the method

Write down the method, tools, mate­ri­als, lay­out and work­ing con­di­tions. Tim­ing should only begin once the method is proper and set­tled.

3. Break the job into ele­ments

An ele­ment is a dis­tinct part of the job with clear start and end points (break points). For car­ton pack­ing the ele­ments could be: fold car­ton, place items, seal, label. Ele­ments make obser­va­tion eas­ier, sep­a­rate machine-con­trolled from worker-con­trolled parts, show where the time goes and allow ele­ment times to be reused as stan­dard data.

4. Time the ele­ments over sev­eral cycles

With the con­tin­u­ous (cumu­la­tive) method the watch runs through­out and read­ings are sub­tracted after­wards; with the snap-back (fly­back) method the watch is reset to zero after every ele­ment. Sev­eral cycles are timed, and abnor­mal read­ings caused by unusual events, such as a dropped tool, are excluded from the aver­age.

5. Decide the num­ber of cycles

More cycles give more con­fi­dence. A com­mon for­mula for the num­ber of obser­va­tions, for 95 per cent con­fi­dence and an accu­racy of plus or minus 5 per cent, is

$$\displaystyle n = \left(\frac{40\sqrt{N\sum x^2 - \left(\sum x\right)^2}}{\sum x}\right)^2$$

where $N$ is the num­ber of pilot read­ings and $x$ is each read­ing. Alter­na­tively, with a pilot stan­dard devi­a­tion $s$ and mean $\bar{x}$, $\displaystyle n = \left(\frac{z s}{a \bar{x}}\right)^2$, where $z$ is the con­fi­dence fac­tor and $a$ the accu­racy as a frac­tion.

6. Rate the work­er's per­for­mance

The ana­lyst com­pares the observed pace with a defined nor­mal pace (100 per cent). A worker judged 10 per cent faster than nor­mal is rated 110; one 10 per cent slower is rated 90. Rat­ing turns the observed time into the time a nor­mal worker would take. Com­mon sys­tems include pace (speed) rat­ing and the West­ing­house lev­el­ling sys­tem, which con­sid­ers skill, effort, con­di­tions and con­sis­tency.

7. Add allowances and set the stan­dard

No one can work con­tin­u­ously like a machine, so allowances are added to nor­mal time.

• Per­sonal allowance: for per­sonal needs such as drink­ing water or using the wash­room.
• Fatigue (relax­ation) allowance: for recov­ery from phys­i­cal and men­tal effort; it rises with heavy work, heat, noise or monot­ony.
• Process (unavoid­able delay) allowance: com­pen­sates for machine wait­ing or process delays out­side the work­er's con­trol.
• Con­tin­gency, pol­icy or spe­cial allowances: for small, irreg­u­lar extra work, or set by man­age­ment pol­icy.

Per­sonal and fatigue allowances together are often called PF allowances, and a com­bined total of about 10 to 20 per cent is com­mon in text­book prob­lems.

The for­mu­las

$$\displaystyle \text{Observed time (OT)} = \frac{\sum \text{readings}}{\text{number of cycles}}$$

$$\displaystyle \text{Normal time (NT)} = OT \times \frac{\text{Rating}}{100}$$

$$\text{Standard time (ST)} = NT \times (1 + A)$$

Here $A$ is the allowance expressed as a frac­tion of nor­mal time. When allowances are instead given as a frac­tion of the total work­ing day, the for­mula becomes $\displaystyle ST = \frac{NT}{1 - A}$. Read the ques­tion care­fully to see which basis is intended.

Worked exam­ple: stan­dard time for car­ton pack­ing

Sup­pose a pack­ing unit (hypo­thet­i­cal fig­ures) times a packer over five cycles. Read­ings are in min­utes. Allowances are 15 per cent of nor­mal time, and the wage is ₹180 per hour.

Step 1: observed (aver­age) time for each ele­ment.

$$\displaystyle OT_A = \frac{1.00}{5} = 0.200 \quad OT_B = \frac{1.75}{5} = 0.350 \quad OT_C = \frac{1.25}{5} = 0.250 \quad OT_D = \frac{0.75}{5} = 0.150$$

Step 2: nor­mal time for each ele­ment.

$$NT_A = 0.200 \times 1.10 = 0.220 \qquad NT_B = 0.350 \times 1.00 = 0.350$$

$$NT_C = 0.250 \times 0.90 = 0.225 \qquad NT_D = 0.150 \times 1.20 = 0.180$$

Step 3: total observed and nor­mal time per car­ton.

$$\displaystyle \sum OT = 0.200 + 0.350 + 0.250 + 0.150 = 0.950 \text{ min}$$

$$\displaystyle \sum NT = 0.220 + 0.350 + 0.225 + 0.180 = 0.975 \text{ min}$$

Rat­ing has added $0.975 - 0.950 = 0.025$ minute.

Step 4: stan­dard time.

$$ST = 0.975 \times 1.15 = 1.12125 \approx 1.121 \text{ min per carton}$$

The allowances add $0.975 \times 0.15 = 0.14625 \approx 0.146$ minute.

Step 5: stan­dard out­put per 8-hour shift.

$$\displaystyle \frac{8 \times 60}{1.12125} = \frac{480}{1.12125} = 428.1 \approx 428 \text{ cartons}$$

Step 6: stan­dard labour cost per car­ton. At ₹180 per hour, labour costs $\displaystyle \frac{180}{60} = 3$ rupees per minute, so the stan­dard labour cost is $1.12125 \times 3 = 3.36$ rupees, or about ₹3.36 per car­ton.

If the allowance had been stated as 15 per cent of the work­ing day instead, the stan­dard time would be $\displaystyle \frac{0.975}{1 - 0.15} = 1.147$ min­utes, which shows why the basis mat­ters.

Work sam­pling

Work sam­pling (activ­ity sam­pling), devel­oped by L. H. C. Tip­pett in the British tex­tile indus­try, esti­mates the pro­por­tion of time spent on dif­fer­ent activ­i­ties from a large num­ber of ran­dom, instan­ta­neous obser­va­tions. At each ran­dom moment the observer sim­ply notes whether the worker is work­ing or wait­ing, or whether the machine is run­ning or idle.

Worked exam­ple: machine util­i­sa­tion

Sup­pose an observer makes 400 ran­dom obser­va­tions of a pack­ing machine over two weeks and finds it run­ning in 340 of them.

$$\displaystyle \hat{p} = \frac{340}{400} = 0.85$$

The machine is esti­mated to be run­ning 85 per cent of the time and idle 15 per cent. In a 480-minute shift that means about $0.15 \times 480 = 72$ idle min­utes. To be 95 per cent con­fi­dent that the esti­mate is within plus or minus 3 per­cent­age points ($e = 0.03$, $z = 1.96$), the num­ber of obser­va­tions needed is

$$\displaystyle n = \frac{z^2 \hat{p}(1 - \hat{p})}{e^2} = \frac{1.96^2 \times 0.85 \times 0.15}{0.03^2} = \frac{0.4898}{0.0009} = 544.2$$

so at least 545 obser­va­tions are required; the 400 already taken are not enough for that accu­racy.

Appli­ca­tions

Man­u­fac­tur­ing

Pack­ing, machin­ing, assem­bly (for exam­ple, the time to assem­ble one switch­board unit), inspec­tion, load­ing and unload­ing, and other repet­i­tive oper­a­tions.

Ser­vices

Patient reg­is­tra­tion in a hos­pi­tal, pro­cess­ing a bank form, billing at a store counter, han­dling files in an office, order pick­ing in a ware­house and admis­sion work in a school.

Work mea­sure­ment, incen­tives and pro­duc­tiv­ity

Incen­tive schemes need a fair def­i­n­i­tion of expected out­put. If the stan­dard for a car­ton is 1.121 min­utes, a worker pro­duc­ing more than 428 car­tons in a shift has beaten the stan­dard and can be paid a bonus. With­out mea­sured stan­dards, incen­tive schemes are arbi­trary and often dis­puted. Mea­sured time also improves pro­duc­tiv­ity because it reveals delays, sup­ports bet­ter sched­ul­ing, exposes under­used capac­ity and helps bal­ance work across sta­tions and staff.

Ben­e­fits and prob­lems

Con­di­tions for a suc­cess­ful study

• the method is improved and fixed before tim­ing
• the worker under­stands the pur­pose
• the ana­lyst is trained and impar­tial
• enough cycles are observed
• allowances are fair and clearly stated
• man­age­ment uses the results for improve­ment, not harass­ment

Key terms

Work mea­sure­ment

Tech­niques for estab­lish­ing the time for a qual­i­fied worker to do a spec­i­fied job at a defined level of per­for­mance.

Time study

Tim­ing and rat­ing the ele­ments of a job to estab­lish its stan­dard time.

Ele­ment

A dis­tinct part of a job with clear break points, timed sep­a­rately.

Observed time

The aver­age of the valid stop­watch read­ings for an ele­ment or job.

Per­for­mance rat­ing

The ana­lyst's assess­ment of the work­er's pace against nor­mal pace, as a per­cent­age.

Nor­mal time

Observed time mul­ti­plied by the rat­ing fac­tor.

Allowances

Extra time for per­sonal needs, fatigue and unavoid­able delays.

Stan­dard time

Nor­mal time plus allowances; the time allowed for the job.

Work sam­pling

Esti­mat­ing the share of time in each activ­ity from ran­dom instan­ta­neous obser­va­tions.

PMTS

Pre­de­ter­mined motion time sys­tems, which build job times from pub­lished times for basic motions.

Com­mon ques­tions

What is the dif­fer­ence between nor­mal time and stan­dard time?

Nor­mal time is the observed time adjusted to a nor­mal pace by rat­ing. Stan­dard time is nor­mal time plus allowances for per­sonal needs, fatigue and delays. In the exam­ple, nor­mal time is 0.975 minute and stan­dard time is 1.121 min­utes.

Why is per­for­mance rat­ing nec­es­sary?

Observed work­ers do not all work at the nor­mal pace. With­out rat­ing, tim­ing a fast worker would give a stan­dard that is too tight and tim­ing a slow worker one that is too loose.

Are allowances added to observed time or nor­mal time?

To nor­mal time. Rat­ing is applied first, then allowances. Check whether the allowance is a per­cent­age of nor­mal time, $ST = NT(1 + A)$, or of the work­ing day, $\displaystyle ST = \frac{NT}{1 - A}$.

What does the process allowance cover?

It com­pen­sates the worker for machine wait­ing or process delays that are out­side the work­er's con­trol.

When is work sam­pling pre­ferred to time study?

When jobs are long, irreg­u­lar or spread across many peo­ple or machines, or when the ques­tion is how much time is idle or pro­duc­tive rather than how long one cycle takes.

Why should method study come before time study?

Tim­ing a waste­ful method builds the waste into the stan­dard. The method is improved first, and then its time is mea­sured.

Ref­er­ences

1. Kanawaty, G. (ed.) Intro­duc­tion to Work Study. Inter­na­tional Labour Office, Geneva.
2. Tay­lor, F. W. (1911) The Prin­ci­ples of Sci­en­tific Man­age­ment. Harper & Broth­ers.
3. Steven­son, W. J. Oper­a­tions Man­age­ment. McGraw-Hill Edu­ca­tion.
4. Chase, R. B. and Jacobs, F. R. Oper­a­tions and Sup­ply Chain Man­age­ment. McGraw-Hill Edu­ca­tion.
5. Pan­neer­sel­vam, R. Pro­duc­tion and Oper­a­tions Man­age­ment. PHI Learn­ing.

Related read­ing

• Method Study in Oper­a­tions Man­age­ment
• Qual­ity Man­age­ment in Oper­a­tions Man­age­ment
• Sta­tis­ti­cal Qual­ity Con­trol in Oper­a­tions Man­age­ment