MIL-HDBK-231A, MILITARY HANDBOOK ENCODERS SHAFT ANGLE TO DIGITAL. This handbook describes the operation of contact and non- contact (formerly brush and brushless) shaft-position, analog-to-digital encoders. It contains physical descriptions and illustrations of encoders, techniques used, theory of operation, background information on binary codes, coding principles and limitation, definitions of encoder terminology, and other criteria for selecting an encoder including identification and marking of encoders for military use.