Information in the Chart Headings

Hours to program & test 1 module
Actual time - Estimated time
0 +/- 7 hours
Sampling Frequency
All modules

The Chart headings tell us that the characteristic under investigation is the difference between the time it was estimated that the module would take to develop and the time it actually took (ie. deviation from target).

The specification or tolerance to which the development team is working is 0 ±7 man hours. The figure of 0 represents the nominal (target) value.

The specification, therefore, is that the actual amount of time taken to develop each module should not vary from the target time by more than 1 working day. The indvidual X values on the chart will record the amount by which each module differs from the target.