FIELD: well logging; applicable in measuring of depth of downhole instrument lowering. SUBSTANCE: method includes application with clock interval L to armor of load-carrying logging cable of sections with different magnetization intensity whose sequence is used for presenting compound magnetic marks. Located along moving logging cable with clock interval L is row of n readout devices with formed, at each output of said devices, corresponding signal proportional to magnetization intensity of section of logging cable armor passing corresponding readout device. Number n of readout devices in row equals number of said sections with different magnetic marks. Installed at readout devices are amplifiers. Coefficients of amplifier transmission are preset so that row from products of amplifier transmission coefficients and corresponding to them readout devices corresponds with accuracy to constant multiple to mirror reflection of known sequence of sections of same magnetization intensity of logging cable armor sections used for presenting compound magnetic marks. Output signals of amplifiers are summarized with help of summarizing unit having n inputs. Output of summarizing unit is connected with input of comparator unit which is connected in series with output unit. In this case, result of summarizing is used as output signal of optimal matched filter. EFFECT: increased noise immunity of detection of compou7nd magnetic marks. 2 cl, 5 dwg
