It is stated that an out-of-round surface having an even number of high-spots requires a checking instrument that has opposed measuring points; and that, if the number of high-spots on the surface is uneven, an instrument having three-point contact, and one of the points of contact located on the center line between the other two, is necessary. Concerning the use of the three-point method, for close work, the angle between the three points of contact must be selected according to the number of high-spots.
Divisions of the subject include types of out-of-roundness and those peculiar to certain machines, the three-point measurnig system, errors of the V-block method, use of the V-block for elliptical objects, other methods of checking elliptical forms and indicator-reading correction. Three items for instrument improvement are suggested to manufacturers.
