Work study: method study and time study

In short

Work study is the systematic examination of how work is done, so that the method is improved (method study) and the time a qualified worker needs for it is measured (time study / work measurement). It is the oldest and cheapest productivity tool in industrial engineering: it needs a stopwatch, charts and discipline rather than capital, and it produces the standard time on which costing, incentive pay, manpower planning, line balancing and capacity calculations all rest. It is examined heavily in GATE (PI and ME, Industrial Engineering section) and in every university Industrial Engineering paper, usually as numericals on normal time, standard time, number of observations and work sampling. Indian employers — Maruti Suzuki, Tata Motors, Bajaj, TVS, Hero, Bosch, L&T, Godrej, Amul, Flipkart and Amazon warehouses, textile and garment units in Tiruppur and Ludhiana — recruit Industrial Engineers and "IE/Time Study" officers specifically for this work. The standard reference in India is the ILO's *Introduction to Work Study*; certification is offered by the Indian Institution of Industrial Engineering (IIIE) and training by NITIE, Mumbai (now IIM Mumbai).

Explained

What work study is and how the two halves fit together

• Work study = method study + work measurement. Method study comes first (improve the method), work measurement second (time the improved method). Timing a bad method only standardises waste.
• Objectives: raise productivity without extra investment, reduce fatigue and unnecessary movement, standardise the method, set fair standards, and give data for planning and costing.
• Productivity = output / input. Work study raises it by removing ineffective time — time wasted by management (bad design, poor layout, no planning, breakdowns) and by the worker (late starts, careless work, accidents).
• Who does it: the work-study officer records facts; the method is changed with the supervisor's and operator's agreement. Without worker and union consent, work study fails — this is the single most stressed "human aspect" point in exams.
• Scope limits: it cannot fix a wrong product design, a wrong process choice, or a wrong plant location; those belong to value engineering and facility planning.

Method study — steps and recording techniques

Remembered as SREDDIM (seven steps; the ILO's eight-step list separates Evaluate from Define): Select → Record → Examine → Develop → Define (evaluate and define) → Install → Maintain.

1. Select the job on economic grounds (high cost, high volume, bottleneck), technical grounds (quality, new technology) and human grounds (fatiguing, unsafe, unpopular work).
2. Record the present method in full, using standard charts and diagrams (below).
3. Examine critically with the questioning technique — primary questions on *purpose* (what is done, why), *place*, *sequence*, *person*, *means*; then secondary questions (what else could be done, and what should be done). The answers drive ECRS: Eliminate, Combine, Rearrange (re-sequence), Simplify.
4. Develop the improved method with the operator and supervisor; check cost, safety and quality.
5. Define it in a written standard operating procedure, with a layout sketch and tooling list.
6. Install — train operators, trial-run, resolve resistance.
7. Maintain — audit periodically; methods drift back within weeks if unchecked.

Recording techniques (charts use the five standard process-chart symbols — operation ○, transport →, inspection □, temporary delay D, permanent storage ▽; a combined activity is shown by overlapping symbols):

• Outline (operation) process chart: only operations and inspections — a bird's-eye view of the whole process.
• Flow process chart: all five symbols, with distance and time; made in material type, man type or equipment type — never mix the subject in one chart.
• Two-handed (left-hand right-hand) process chart: bench-level work, both hands charted on the same time scale; symbols reduced to operation, transport, hold, delay.
• Multiple activity chart: worker(s) and machine(s) on a common time scale — exposes idle time, and is the basis of man-machine and crew balancing.
• SIMO (simultaneous motion cycle) chart: therbligs of both hands against a film/video time scale (in winks, 1/2000 min, or in frames) — the finest level.
• Diagrams: flow diagram (path of material on a scaled layout), string diagram (thread and pins to measure travel for irregular, repetitive movement), travel/from-to chart (matrix of movements between stations), cycle graph and chronocycle graph (light trace on a photograph; the chronocycle's pear-shaped dashes show direction and speed), 3-D models.
• Film techniques: micromotion study (normal or high speed, for short repetitive cycles), memomotion study (slow — about 1 frame/s or /min — for long cycles and team/materials movement).

Motion study, therbligs and motion economy

• Motion study is the microscopic part of method study: analysis of the operator's individual movements at a workplace.
• Therbligs (Frank and Lillian Gilbreth; "Gilbreth" nearly reversed) are 17 basic elements, 18 with *find*: search, find, select, grasp, reach (transport empty), move (transport loaded), hold, release, position, pre-position, inspect, assemble, disassemble, use, unavoidable delay, avoidable delay, plan, rest to overcome fatigue. Effective therbligs do the work; ineffective ones (search, select, hold, delays, plan) are the targets for elimination.
• Principles of motion economy — three groups:
  • *Use of the human body:* both hands should begin and end motions together, work symmetrically and in opposite directions, never be idle at the same time; motions should be continuous and curved, not zig-zag with sharp reversals; use momentum; use the lowest adequate classification of movement (finger → wrist → forearm → upper arm → shoulder/trunk); ballistic motions are faster and less fatiguing than controlled ones.
  • *Workplace arrangement:* fixed locations for all tools and materials; locate them close in front of the operator within normal and maximum working areas; use gravity feed bins and drop-delivery chutes; provide correct illumination and a chair-and-table height allowing sitting or standing.
  • *Design of tools and equipment:* relieve the hands with jigs, fixtures and foot-operated devices; combine two tools into one; pre-position tools; use levers, cranks and handwheels positioned for least body movement.
• Ergonomics extends this to anthropometry, posture, lighting, noise, heat and manual-handling limits — the legal hook in India is the duty of the employer to provide a safe working environment under the Occupational Safety, Health and Working Conditions Code, 2020, in force from 21 November 2025, which replaced the Factories Act, 1948.

Work measurement — techniques and time study procedure

Techniques: (a) time study (stopwatch), (b) work sampling (ratio delay), (c) predetermined motion time systems (PMTS), (d) synthetic/standard data, (e) analytical estimating, (f) historical records (least reliable).

Stopwatch time study, step by step:

1. Select the job and inform the operator; study a qualified, average operator on the approved method.
2. Record all job, operator, machine, tool and condition details.
3. Break the job into elements — each with clear start and end points ("break points"), normally 0.04–0.5 min long. Element types: repetitive, occasional, constant, variable, manual, machine (machine-controlled), governing, foreign.
4. Decide the number of cycles statistically (formula below) or from standard tables.
5. Time each element with a decimal-minute stopwatch (1 division = 0.01 min) or decimal-hour watch (0.0001 h), using the continuous (cumulative) method — watch runs throughout, readings subtracted later — or the snapback (fly-back/repetitive) method — reset at each break point. Continuous is more accurate and records all delays; snapback is easier to compute but loses time in resetting.
6. Rate the performance of the operator against standard performance on each element (not once for the whole study).
7. Normal (basic) time = observed time × rating / 100.
8. Add allowances to get standard (allowed) time.
9. Publish the standard with the method it belongs to; it becomes invalid the moment the method, tooling or material changes.

Performance rating — judging the operator's pace against a defined standard pace (on the British Standard 0–100 scale, 100 = standard performance of a motivated qualified worker on incentive, often illustrated as walking 4.8 km/h or dealing 52 cards into four piles in 0.5 min; the older 60–80 and 75–100 scales also appear).

• Speed (pace) rating: single judgement of speed — the most used.
• Westinghouse (Lowry-Maynard-Stegemerten) system: four factors — skill, effort, conditions, consistency — each with a tabled plus/minus value; sum added to 1.00.
• Synthetic rating: compare observed times of some elements with PMTS values to compute a rating factor, then apply it to the rest.
• Objective rating: rate speed only, then apply a separate job-difficulty adjustment.
• Rating is the most subjective and most disputed step; consistency is trained with rating films.

Allowances (added to normal time, ILO practice):

• Relaxation allowance = fixed (personal needs ~5–7%, basic fatigue ~4%) + variable (abnormal posture, force, heat and humidity, bad light, noise, mental strain, monotony).
• Contingency allowance — small, infrequent, legitimate extras (typically ≤5%).
• Process / unavoidable delay allowance — operator idle while the machine works.
• Special allowances: set-up, tool change, cleaning, start-up/shut-down, learning, policy allowance (a management decision, not a work-study value — keep it separate).
• Interference allowance for multi-machine work. Exact percentages are a matter of company and industry agreement; there is no statutory table.

Work sampling, PMTS and synthetic data

• Work sampling (ratio-delay / activity sampling): a large number of instantaneous, random observations; the proportion of observations in an activity estimates the proportion of time spent on it, by the law of statistical sampling. Observations must be random (use random number tables for observation times) and the observer must record what is happening *at the instant* of arrival.
  • *Advantages:* covers many operators/machines at once, cheap, no stopwatch, no continuous presence, less resented, easily interrupted and resumed.
  • *Limitations:* not economical for short-cycle jobs, gives no element breakdown or method detail, needs rating of pace if a standard time is wanted, and large samples for small percentages.
• Predetermined Motion Time Systems (PMTS): tabulated normal times for basic motions; the analyst synthesises the time from the motion pattern without timing anyone.
  • MTM-1 (reach, move, turn, grasp, position, release, disengage, eye travel, body motions) in TMU: 1 TMU = 0.00001 h = 0.0006 min = 0.036 s. MTM-2 and MTM-3 are faster, coarser versions; MOST (BasicMOST, MiniMOST, MaxiMOST, AdminMOST) uses activity sequences; Work-Factor and BMT are other families.
  • *Advantages:* no rating needed, set before production starts, consistent, good for method comparison and workstation design. *Limitations:* costly training, data valid only for manual, non-machine-paced work, not suited to very long or heavy irregular jobs.
• Synthetic (standard) data: element times built up from a company's own past studies — fast, consistent, and the usual basis for estimating on new jobs and for CAM/ERP routing times.
• Analytical estimating: experienced estimator uses synthetic data plus judgement for one-off and maintenance jobs.
• Uses of standard time: manpower requirement, machine capacity and loading, line balancing and cycle time, scheduling, standard cost and quotation, incentive schemes (piece rate, Halsey, Rowan), budget and efficiency measurement (worker efficiency = standard hours earned / actual hours worked).

Indian legal and standards context

• Working time is governed by the Code on Wages, 2019 and the OSH&WC Code, 2020, both in force from 21 November 2025, which replaced the Factories Act, Minimum Wages Act, Payment of Wages Act and BOCW Act (the Industrial Disputes Act was replaced by the Industrial Relations Code, 2020). The usual framework is 8 hours a day and 48 hours a week as normal working hours, with overtime paid at twice the ordinary rate of wages, a rest interval after about 5 hours of continuous work, and a weekly off. Exact spread-over, overtime ceilings and the permissibility of 12-hour shifts (within 48 hours a week) are set in central and state rules and therefore vary by state — check the applicable state rules rather than quoting a single number.
• Industrial relations: changing a standard time or an incentive scheme alters service conditions; under the Industrial Relations Code, 2020 such changes require due notice to workers, so time standards are normally settled with the union.
• Standards: work-study charting in India follows the ASME/ILO five-symbol convention; ergonomics and anthropometric data for Indian users are covered by BIS standards on ergonomics and human factors — quote the current IS number from the BIS catalogue, as several older numbers have been revised or withdrawn. ISO 9001 clause requirements on documented procedures make the *defined method* an auditable record.

Key points

• Work study - method study (improve the method) plus work measurement (time the improved method); method study always first.
• SREDDIM - Select, Record, Examine, Develop, Define, Install, Maintain: the seven steps of method study (the ILO's eight-step version separates Evaluate from Define).
• ECRS - Eliminate, Combine, Rearrange, Simplify: the hierarchy of improvement after critical examination.
• Five chart symbols - operation, transport, inspection, delay, storage; a flow process chart must stick to one subject (man, material or equipment).
• String diagram - measures distance travelled in irregular, repetitive movement; flow diagram shows the path on a scaled layout.
• Multiple activity chart - worker and machine on a common time scale; the tool for exposing and balancing idle time.
• Therbligs - 17 (18 with *find*) basic hand motions; eliminate the ineffective ones: search, select, hold, delays, plan.
• Motion economy - three groups: human body, workplace arrangement, tool and equipment design; use the lowest adequate movement class.
• Micromotion vs memomotion - fast film for short cycles; slow film (1 frame/s or /min) for long cycles and crew work.
• Qualified worker - the standard is set on an average qualified operator on the approved method, not on the fastest or slowest.
• Normal time = observed time × rating/100; standard time = normal time + allowances.
• Rating - pace judged against 100 on the BS scale; Westinghouse rates skill, effort, conditions and consistency.
• Allowances - relaxation (fixed personal + basic fatigue, plus variable), contingency, process delay, special and policy; policy allowance is a management decision, kept separate.
• Continuous vs snapback timing - continuous captures all time and is more accurate; snapback is simpler but loses reset time.
• Number of cycles - fixed statistically from the observed variability and the accuracy and confidence required, not by habit.
• Work sampling - random instantaneous observations; good for idleness/utilisation studies and many subjects at once, useless for element detail.
• PMTS (MTM, MOST) - synthesised normal times in TMU (1 TMU = 0.036 s), no rating needed, valid only for manual, non-machine-paced work.
• A standard time dies with its method - any change in method, tooling, material or layout requires a restudy.

Formulas and examples

Example 1 — standard time and standard output. Ten observed cycle times (min): 1.22, 1.18, 1.25, 1.20, 1.30, 1.15, 1.24, 1.21, 1.19, 1.26. Rating 110%. Allowances 15% of normal time. Shift = 8 h with 480 working minutes.

• Σx = 12.20 min → OT = 12.20/10 = 1.220 min
• NT = 1.220 × 1.10 = 1.342 min
• ST = 1.342 × 1.15 = 1.543 min per piece
• Standard output = 480 / 1.543 ≈ 311 pieces per shift
• If instead the 15% were expressed as a fraction of standard time: ST = 1.342/0.85 = 1.579 min, output = 480/1.579 ≈ 304 pieces — a 2% difference, which is why the convention must be stated.

Example 2 — how many cycles are needed? Same ten readings, ±5% accuracy at 95% confidence.

• Σx² = 14.9012; Σ(x − x̄)² = 14.9012 − (12.20)²/10 = 14.9012 − 14.884 = 0.0172
• s = √(0.0172/9) = 0.0437 min
• n = (1.96 × 0.0437 / (0.05 × 1.220))² = (0.0857/0.0610)² = 1.405² ≈ 2 cycles
• By the 40-constant form: 40√(10 × 14.9012 − 148.84)/12.20 = 40 × 0.4147/12.20 = 1.36 → n ≈ 2. The ten readings already exceed the requirement, because this element is very consistent.

Example 3 — work sampling accuracy. A study of a CNC section takes 2,000 random observations; the machine is idle in 400 of them.

• p = 400/2000 = 0.20 (20% idle)
• Absolute accuracy at 95%: e = 1.96 √(0.20 × 0.80 / 2000) = 1.96 × 0.00894 = 0.0175 → idle time = 20% ± 1.75% (confidence interval 18.25% to 21.75%)
• To get ±5% *relative* accuracy (i.e. ±1% absolute): n = 1.96² × 0.80 / (0.05² × 0.20) = 3.8416 × 0.80 / 0.0005 = 6,147 observations — showing how costly tight accuracy on a small percentage becomes.

Example 4 — standard time from a work-sampling study. One operator is observed over 5 shifts of 8 h (total 2,400 min). Of 2,000 observations, 1,500 show her working on the job; 1,200 units are produced; average rating 95%; allowances 12%.

• Working time on the job = 2,400 × (1500/2000) = 1,800 min
• Normal time per unit = 1,800 × 0.95 / 1,200 = 1.425 min
• ST = 1.425 × 1.12 = 1.596 min per unit

Example 5 — justifying a method-study change. A fixture costing ₹60,000 cuts the standard time of an assembly from 2.50 min to 1.90 min. Output is 1,000 units/day, 300 working days, labour cost ₹150 per operator-hour, 480 productive minutes per operator-shift.

• Time saved = 0.60 min × 1,000 = 600 min/day = 10 operator-hours/day
• Saving = 10 × ₹150 = ₹1,500/day → ₹1,500 × 300 = ₹4.5 lakh/year
• Payback = 60,000/1,500 = 40 working days
• Operators needed: before = 1,000 × 2.50/480 = 5.21 → 6; after = 1,000 × 1.90/480 = 3.96 → 4 (two operators redeployed)

Example 6 — PMTS. An MTM-1 analysis of a small assembly totals 420 TMU; allowances 13%.

• NT = 420 × 0.036 s = 15.12 s = 0.252 min
• ST = 0.252 × 1.13 = 0.285 min → output = 480/0.2848 ≈ 1,685 pieces/shift

Where it is used

• Automobile and auto-component plants: cycle time and standard time for every station on the assembly line, line balancing and manpower per shift — Maruti Suzuki, Tata Motors, Hyundai, Bajaj, TVS, Bosch, Sundram Fasteners; "IE / Time Study Engineer" and "Productivity Engineer" are standing job titles.
• Garment and textile manufacturing (Tiruppur, Ludhiana, Bengaluru): SAM (standard allowed minutes) per style drives line setting, operator target, piece rate and costing; GSD/PMTS systems are common for sewing operations.
• Warehousing, e-commerce and logistics: pick-pack-dispatch standards and productivity targets at Flipkart, Amazon India, DMart and Reliance Retail distribution centres; work sampling for equipment and dock utilisation.
• Services and back offices: BPO/BFSI transaction handling times, hospital nursing-activity sampling, Indian Railways and postal counter staffing, municipal workload studies.
• Maintenance and project work: analytical estimating and synthetic data for job-card times in refineries, power plants, L&T and BHEL workshops.
• Lean manufacturing and Kaizen: method study is the ancestor of standardised work, takt time, SMED and the seven-wastes exercise used in every TPM/lean rollout; work study also feeds routing times into ERP (SAP PP) and MES.

Interview questions

• Q: Why must method study precede time study? A: Time study sets a standard for the method in front of it; timing an unimproved method standardises existing waste and makes the inefficiency permanent.
• Q: What exactly is the difference between normal time and standard time? A: Normal time is the observed time corrected for the operator's pace by the rating factor; standard time is normal time plus allowances for relaxation, contingency and unavoidable delay, so it is the time actually allowed in practice.
• Q: What is rating and why is it the weakest link? A: Rating is the observer's judgement of the operator's pace against standard performance (100 on the BS scale); it is a human estimate, so two observers can differ, and it is the usual subject of dispute with unions — rating films and the Westinghouse factor method are used to improve consistency.
• Q: How do you decide the number of cycles to time? A: From a trial study: compute the mean and standard deviation of the readings and use n = (z·s/(e·x̄))², typically z = 1.96 and e = 0.05 — variable elements need many more cycles than constant ones.
• Q: When would you choose work sampling over a stopwatch study? A: When you want utilisation or idleness over many machines or operators, for long or non-repetitive cycles, or when continuous observation is impractical or resented; not when you need element-level times for a short-cycle job.
• Q: How many random observations does work sampling need? A: From n = z²p(1−p)/e²; for p = 0.2 and ±1.75% absolute accuracy at 95% confidence about 2,000 observations suffice, but ±1% absolute needs roughly 6,100.
• Q: What are therbligs and which ones do you attack first? A: The 17 (or 18) basic hand motions defined by the Gilbreths; the ineffective ones — search, select, hold, avoidable and unavoidable delay, plan — are eliminated first, usually by fixed locations, pre-positioning and fixtures that replace "hold".
• Q: Difference between a flow diagram and a string diagram? A: A flow diagram draws the path of material or worker on a scaled layout; a string diagram uses thread on pins on a scaled layout to measure total distance travelled in irregular repetitive movement, so alternative layouts can be compared numerically.
• Q: What is a policy allowance and why is it kept separate? A: An extra percentage granted by management for reasons outside work study (for example to protect earnings during a changeover); it is not a measured value, so mixing it into relaxation allowance corrupts the standard and hides the decision.
• Q: An operator finishes 10 units in 8 hours against a standard time of 40 min each. What is her efficiency? A: Standard hours earned = 10 × 40/60 = 6.67 h against 8 h worked, so efficiency ≈ 83%.
• Q: Why does PMTS need no rating? A: The tabulated TMU values are already normal times for basic motions performed at standard pace, so the synthesised time is a normal time by construction — only allowances are added.
• Q: The union says the new standard is unfair. How do you respond? A: Show the recorded method, element breakdown, rating basis and allowance build-up, re-study jointly with their representative on an agreed qualified operator, and check that the installed method, tooling and material match the method that was timed.
• Q: A standard time was set two years ago; the operator now beats it by 40%. What do you check first? A: Whether the method has changed — new tooling, better material, a layout change or an informal shortcut; if so the standard is invalid and the job must be restudied, not merely tightened.

Common mistakes

• Confusing observed, normal and standard time, or multiplying by the rating twice; also applying one rating to the whole study instead of element by element.
• Mishandling the allowance convention — taking a percentage *of standard time* as if it were *of normal time* (use ST = NT/(1 − A′) only when the allowance is defined on standard time).
• Mixing the chart subject: putting the man's movements and the material's movements in the same flow process chart.
• Timing the fastest or the slowest operator, or an operator who is being watched for the first time, instead of a qualified worker on the approved method.
• Taking work-sampling observations at regular intervals or at convenient times — it destroys randomness and biases the result; and quoting a percentage without its confidence limits or the number of observations.
• Dropping readings that merely look high: only genuinely abnormal readings with an identified cause (dropped tool, interruption) may be excluded, and the reason must be recorded.
• Unit slips — decimal minutes read as seconds, TMU not converted (1 TMU = 0.036 s), or forgetting that standard output uses *productive* minutes per shift, not 8 × 60 of clock time.
• Treating a standard time as permanent, and ignoring the consent and communication steps, which is the commonest practical reason work-study schemes fail on the shop floor.

Related topics

• Plant layout and material handling · Production planning and control · Scheduling and sequencing · Operations research basics · Queuing theory and simulation · Ergonomics, lean manufacturing and wage incentive schemes