Stopwatch time study

In one line

Timing well is not just pressing a button: you have to choose how the time of each element is recorded, how many cycles to observe and how to avoid reading errors.

The equipment

Niebel and Freivalds mention two types of stopwatch. The traditional decimal-minute stopwatch has a dial with 100 divisions, each worth 0.01 minutes, so one full turn of the long hand takes one minute; the short hand marks the minutes. The electronic stopwatch has a resolution of 0.001 seconds and can time any number of elements while it keeps counting the total time; that is why it delivers both continuous and return-to-zero times without the drawbacks of mechanical ones. The book notes that electronic stopwatches are gradually replacing mechanical ones. In addition, video cameras are ideal for recording the operator's method and the elapsed time, and they allow you to study the operation frame by frame.

Two ways to record

With either method, at the start of the study you write down the time on a master clock and start the stopwatch; after that, you read it at the break point of each element (the instant when one ends and the next begins).

	Continuous method	Return-to-zero method
How it works	The stopwatch runs during the whole study; you read it at each break point without stopping it	You read it at each break point and return the stopwatch to zero; the next element starts from zero
Element time	Obtained by subtracting successive readings	It is the direct reading
Main advantage	Leaves a complete record of the whole period: delays and foreign elements are visible	No subtraction is needed, and an element done out of sequence can be recorded right away
Risk	Subtraction errors	Omits delays and foreign elements; short elements are hard to measure; it tempts you to "pick out" individual elements
Best suited for	Short cycles and very short elements	Long elements

Niebel and Freivalds consider the continuous method superior for several reasons: it presents a complete record of the observed period, which gives the operator and the union confidence ("no times were left out of the study"), it is easier to explain, and it is better suited to very short elements. With practice, a good analyst can accurately capture three consecutive short elements, each under 0.04 minutes, if they are followed by one of about 0.15 minutes or more, by remembering the readings at the break points. On the other side, they warn about returning to zero: the elements cannot be studied independently because the time of one element depends on the ones before and after it, and it is a mistake to use the cycles already observed to decide how many additional cycles to study, because it can lead to a sample that is too small.

How many cycles to observe

Niebel and Freivalds reproduce a rough guide from General Electric, based on cycle time:

Cycle time (minutes)	Recommended cycles
0.10	200
0.25	100
0.50	60
0.75	40
1.00	30
2.00	20
2.00 to 5.00	15
5.00 to 10.00	10
10.00 to 20.00	8
20.00 to 40.00	5
40.00 or more	3

The book clarifies that, since a time study is a sampling procedure, a more exact number can be calculated with statistics (from the average and the standard deviation of the readings), but for economic reasons the analyst cannot depend on that alone.

Try it

Real example

Two figures in the book show the same type of sheet with different methods: a study of a die casting operation with returns to zero, and one of a machining operation with continuous times. The logic of the sheet is the same: elements in the columns, cycles in the rows and, for each reading, the observed time and the pace rating. One check the book always asks for is the recording error: the difference between the total stopwatch time and the actual elapsed time, measured with the master clock, which must be less than 2%; if it is exceeded, the study must be repeated. With continuous times, the last stopwatch reading has to match the end time, which lets you verify the study in one go.

A simple illustration, with made-up numbers: with the continuous method, the readings at the three break points of a cycle are 8, 20 and 47 hundredths of a minute, and the element times come out by subtraction: 8, 12 (20 minus 8) and 27 (47 minus 20). With return to zero, the direct readings would have been 8, 12 and 27.

Template to use

A minimal observation sheet includes:

• Operation, operator and observer, date and start time.
• Description and break point of each element, defined before timing.
• Method chosen (continuous or return to zero) and equipment used.
• For each cycle and element: reading, observed time, pace rating (recorded during the element, following the ILO methodology that the UNGS book covers) and notes on delays or foreign elements.
• End time on the master clock and calculation of the recording error.

That sheet is already built in Excel, with the formulas: download the time study observation sheet. It has a tab for each method, calculates the time of each element, the standard time and the pieces per hour, checks the recording error and tells you how many cycles the guide recommends. The values it comes with are examples: you need to delete them.

Benefits

• A clear recording method reduces errors and arguments about the validity of the study.
• The cycle guide prevents studies that are too short or unnecessarily long.
• Continuous recording conveys transparency to the operators.

Limitations to keep in mind

• It depends on defining the break points well: if they are not clear, two analysts get different results.
• Stopwatch timing works for repetitive tasks; for long or irregular tasks you have to resort to work sampling.
• The cycle table is a rough guide from one company, not a standard.

In summary

To time a task: choose the method (continuous almost always, return to zero for long elements), define the break points, observe the number of cycles that corresponds to your cycle time and always check the recording error. With that data you calculate the standard time.