FIELD: well logging. SUBSTANCE: method includes division of load-carrying cable into pieces of similar lengths. Each piece is marked with numbered magnetic mark with individual nonrecurrent structure with marks distribution over length of marked piece. Said magnetic marks present a sequence of parts of cable armoring with different degrees of magnetization. Samples of signals corresponding to numbered magnetic marks and their numbers are stored. Downhole instrument is attached to end of said cable and lowered into well. During lowering or lifting, magnetic mark is detected on moving cable by its reading out accomplished by reader and number of mark is determined. In so doing, signals corresponding to magnetic marks red out from moving cable are compared with their samples and if signal corresponding to read out magnetic mark is congruent with its sample, number of corresponding sample is considered as number n of detected magnetic mark. For this purpose, reader has unit of matched filtration consisting of matched filters, one filter for each signal corresponding to magnetic mark. In this case, inputs of matched filters serve as inputs of matched filtration unit, and outputs of matched filters serve as outputs of matched filtration unit. With detection of magnetic marks on said cable, boundaries of piece and number of magnetic mark are registered on record of logging curve. Depth of lowering of downhole instrument is calculated by offered mathematical expression. EFFECT: extended functional potentialities of method due to increased accuracy of determination of depth of instrument lowering. 2 cl, 2 dwg
