How many cycles should you time?
Enter the task's cycle time and get the number of cycles recommended by the General Electric guide.
Cycles to time (guide)
60
This is the approximate General Electric guide reproduced by Niebel and Freivalds (table 10.2). The shorter the cycle, the more repetitions are needed for the average to be reliable. With the real scatter of your readings you can refine it with statistics, but this table is enough to get started.
How it works
You enter the task's cycle time and the tool returns how many cycles it is advisable to time, according to the approximate General Electric guide reproduced by Niebel and Freivalds (table 10.2):
| Cycle time (min) | Cycles to observe |
|---|---|
| up to 0.10 | 200 |
| up to 0.25 | 100 |
| up to 0.50 | 60 |
| up to 0.75 | 40 |
| up to 1 | 30 |
| up to 2 | 20 |
| up to 5 | 15 |
| up to 10 | 10 |
| up to 20 | 8 |
| up to 40 | 5 |
| more than 40 | 3 |
It is a guide and not a rule: the book notes that a more exact number can be calculated with statistics from the average and the standard deviation of the readings, but that for economic reasons the analyst does not rely on that alone. The recording methods (continuous and snapback) and the control of the recording error (below 2%) are covered in the article. The observation sheet in Excel already includes both methods and these calculations.
Sources
These are the ones from the article where the theory behind this tool is developed.
Continuous or snapback method? It is in the article Stopwatch time study.