The measurement of distortion: concluding remarks.

The means by which fine measurements can be made and distortions computed have been discussed in this series. However, the fact remains that research of this nature is time consuming and demanding. At every step, and in all machined components, care must be taken to eliminate local inaccuracies. Precalibration, postcalibration, and an ongoing program of maintenance are essential if quality results are to be anticipated. An attempt has been made to introduce automatic reading devices with the ability to compute distortions by having the raw data sent directly to a computer. This latter step can be highly dangerous unless at least one "test case" can be programmed into the system as a check on the data access and computational procedures. These test cases should simulate as closely as possible the actual computational requirements of the system, in order that all program "bugs" be corrected before the research is run. In this area, the GIGO rule, "Garbage in-Garbage out," holds true. Unfortunately, if the computational errors are small and of the order of magnitude of the measured distortions the researcher can accept the results without realizing there is a computational problem.