Experimental investigation of subjective errors in decoding circular diagrams

The subjective error in decoding a circular diagram is a substantial component of the total circular-diagram measurement error. It was found that in measuring roundness irregularities below 1 μ, which corresponds to shape precision I, II, and III of GOST (All-Union State Standard) 10356-63, the subjective decoding error may attain 50% of the measured quantity. This error in measuring roundness irregularities which approach 1μ can be substantially reduced by providing additional expansion steps. The subjective decoding error consists of the error in finding the center and diameter of the basic circumference and of the error in estimating the position of the most distant point from the basic circumference. These are random errors. Numerical characteristics of their statistical distribution have been established for reading errors at ¯So=±0.06 templet divisions, for finding the position of the center at ¯Sc=±0.2 templet divisions, and for determining the diameter of the basic circumference at Sd=+-0.09 templet divisions. It has been established that the decoding of circular diagrams entails the operator in the complicated visual problem of orientation by means of templet scale lines and of tracing one of these lines. His task can be greatly facilitated by altering the design of the templet.