How To Conduct A Time Study: A Technical Guide To Work Measurement And Performance Standards

Conducting a time study requires breaking a job into discrete, measurable elements, timing these elements across multiple cycles, and applying performance rating factors to normalize the data. By incorporating PFD (Personal, Fatigue, and Delay) allowances, organizations can establish a "Standard Time" that serves as the foundational metric for labor costing, production scheduling, and lean process optimization.

Work Measurement Prerequisites and Equipment Checklist

Before beginning a formal time study, the work environment must be stabilized. Conducting a study on a non-standardized process yields volatile data that cannot be used for long-term planning. Ensure the "Method" has been optimized through a motion study—standardizing the sequence of movements and the layout of the workstation—to ensure you are timing the most efficient version of the task.

• Essential Measurement Tools: A digital or mechanical decimal-minute stopwatch is the industry standard, though specialized time-study software or high-frame-rate video cameras are increasingly common for micro-motion analysis.
• Documentation Materials: Observation sheets (or digital templates) pre-populated with element descriptions, clipboards, and reliable writing instruments.
• Calibrated Reference Standards: Access to the Standard Operating Procedure (SOP) for the task and a clear definition of the "Average Qualified Operator" performance level (often designated as 100% or 60 on the Bedaux scale).
• Statistical Benchmarks: Determination of the required confidence level (typically 95%) and the desired accuracy (typically ±5%) to calculate the necessary number of observation cycles.
• Administrative Budget: Allocation of 4 to 8 hours of analytical time for every 1 hour of field observation, depending on the complexity of the element breakdown.

The Systematic Workflow for Industrial Time Studies

Step 1: Define the Task and Standardize the Method

Work measurement is futile if the operator uses different techniques in every cycle. You must first verify that the task follows the established SOP. If no SOP exists, you must create a "Method Description" that details the tools used, the material positioning, and the specific sequence of physical motions.

Pro-Tip: Always inform the operator and their supervisor of the study's purpose. Transparency reduces the "Hawthorne Effect," where workers artificially alter their pace because they are being observed.

Step 2: Break the Task into Discrete Elements

Divide the total job cycle into small, manageable segments called "elements." These elements should be as short as possible but long enough to be timed accurately (usually no less than 0.04 minutes or 2.4 seconds).

1. Identify "Constant" elements (those that take the same time every cycle) versus "Variable" elements (those where time fluctuates based on physical properties like weight or size).
2. Clearly define "Breakpoints"—the exact visual or audible signal that ends one element and begins the next (e.g., the sound of a part hitting a bin).
3. Separate "Manual" elements (worker-controlled) from "Machine" elements (equipment-controlled) to ensure performance rating is only applied to human effort.

Step 3: Observe and Record the Timing

Using either the "Continuous" or "Snapback" timing method, record the duration of each element over multiple cycles. In the continuous method, the watch runs uninterrupted, and you record the cumulative time at each breakpoint; in the snapback method, the watch is reset to zero at every breakpoint.

• Record any "Foreign Elements"—interruptions like a dropped tool or a supervisor's question—and mark them for exclusion from the average calculation.
• Ensure you capture enough cycles to account for natural variance. For a cycle time of 1 to 2 minutes, 20 to 50 observations are generally required for statistical significance.

Step 4: Apply Performance Rating Factors

Because the observed operator may be working faster or slower than a "standard" pace, you must apply a Rating Factor (RF). This is a subjective but expert assessment of the operator's speed and skill relative to your concept of 100% performance.

• If an operator is working 10% faster than a normal pace, assign a rating of 1.10 (or 110%).
• If they are working slower, assign a rating such as 0.90 (90%).
• Calculate the "Normal Time" for each element using the formula: Observed Time × (Rating / 100).

Warning: Never apply a performance rating to machine-controlled elements. A machine's cycle time is fixed; rating it as 110% will result in a standard time that is physically impossible to achieve.

Step 5: Calculate and Integrate PFD Allowances

Normal Time represents the time a worker takes without any interruptions. However, humans require breaks and face unavoidable delays. You must add "Allowances" for Personal needs (restroom, hydration), Fatigue (physical or mental exhaustion over an 8-hour shift), and unavoidable Delays (equipment maintenance, material shortages).

1. Personal Allowance: Usually 5% of the workday.
2. Fatigue Allowance: Varies from 4% for light work to 20% or more for heavy manual labor in extreme heat.
3. Delay Allowance: Based on historical data regarding minor unavoidable interruptions.

Step 6: Determine the Final Standard Time

The Standard Time is the final metric used for production planning. It is the sum of the Normal Times for all elements, adjusted by the total allowance percentage. The standard formula is: Standard Time = Normal Time × (1 + Allowance Percentage). This value represents the amount of time a qualified worker, working at a normal pace, should take to complete the task over the course of a full shift.

Work Measurement Methodology and Technical Specs

The choice of timing methodology significantly impacts the precision and difficulty of the study. The following table compares the two primary manual techniques used in industrial engineering.

Industrial Field Failure Scenarios and Remedial Actions

Inconsistent Breakpoint Identification

• Root Cause: The observer has not defined a sharp, sensory-based end-of-element trigger, leading to overlapping time data between elements.
• Actionable Fix: Re-define breakpoints using audible cues (a click, a thud) or definitive physical movements (hand leaving the lever). Re-train the observer to look for these specific cues before restarting the study.

The "Hawthorne Effect" Distortion

• Root Cause: The operator intentionally slows down to ensure a more "lenient" (longer) standard time, or speeds up due to the pressure of being watched.
• Actionable Fix: Increase the observation duration to allow the operator to return to their natural rhythm. If pacing is obvious, use the "Synthetic Rating" method, comparing the observed time to Predetermined Motion Time Systems (PMTS) like MTM-1 to verify the rating's accuracy.

Statistical Undersampling

• Root Cause: The study was concluded after too few cycles, resulting in a standard time that does not reflect the true variance of the process.
• Actionable Fix: Calculate the Standard Deviation of the observed times. Use the formula N = ((40 * √ (n' * Σx² - (Σx)²)) / Σx)² to determine the mathematically required number of cycles (n) for the desired accuracy. If N is greater than your current sample, continue the observation.

Frequently Asked Questions

What is the difference between Normal Time and Standard Time?

Normal Time is the time it takes an average operator to perform a task at a 100% pace, excluding any breaks or interruptions. Standard Time is the Normal Time plus the PFD (Personal, Fatigue, and Delay) allowances, representing the sustainable output expected over a full workday.

How often should a time study be updated?

A time study remains valid as long as the "Method" remains unchanged. You should conduct a new study if there is a change in tooling, workstation layout, raw material specifications, or if the process undergoes a Kaizen improvement event.

How do I handle "outlier" data points in my observations?

Outliers should only be removed if a "Foreign Element" (an external interruption) was specifically noted during that cycle. If an element was simply slower without a clear cause, it must remain in the data set as it represents natural process variation.

Can I conduct a time study using video instead of a stopwatch?

Yes, video time study is often more accurate because it allows for frame-by-frame analysis and can be reviewed by multiple engineers to ensure consistent performance rating. It also provides a permanent record of the "Method" used at the time of the study.

Optimize Your Operational Efficiency

Establishing rigorous time standards is the first step toward achieving a lean, high-throughput manufacturing environment. Begin your work measurement program today to unlock hidden capacity and ensure your labor costs are competitive and accurate.