FIELD: well logging. SUBSTANCE: method includes preliminary division of loading-carrying logging cable into pieces of similar lengths. Pieces are marked with magnetic marks on cable armoring by distribution of these marks over length of marked piece. Said magnetic marks present a sequence of parts of cable armoring with different degree of magnetization. Downhole instrument is attached to cable end and lowered into well. Magnetic marks are detected on moving cable by their reading out with help of reader. With magnetic marks detected on cable, boundaries of pieces are registered on record of logging curve. Number of detected magnetic marks is determined and depth of lowering of downhole instrument is calculated by offered mathematical expression. EFFECT: extended functional potentialities due to increase of accuracy of determination of downhole instrument lowering depth. 2 dwg
