The Causes of Personal Error in the Coincidence Measurement of the Corner of the Pattern with a Reference Line

Abstract

In precision measurements, the major portion of error is frequently identified as personal error. Such personal error is remarkably seen for example in the measurement of indentation by Vickers indentation measuring equipment, in which the diagonal distance of the magnified image of the indentation must be measured by visual detection of the coincidence of the corner of the image with a reference line. It is the purpose of this paper to derive the theory on the primary causes of the personal error in the detection of the coincidence and to confirm this theory by experiments. In this theory, the error is expressed mathematically using two parameters; minimum noticeable threshold and minimum resolving threshold. A simulator is designed and manufactured in order to prove the theory and to study the characteristics of the personal error in the coincidence measurements. The simulator must satisfy the following requirements: the true touch point can be detected independently of the coincidence measurements and operating procedure is the same as that of actual measurement. Through the series of experiments and studies with two typical coincidence methods, we have reached the conclusion that the error in the coincidence method is to be caused by the personal difference in the above-mentioned threshold values.