Abstract: Method and apparatus for automatically inscribing magnetic marks on a moving wireline are disclosed. An alternating magnetic field is generated for application to a zone on the moving wireline. The marks are inscribed on the wireline by interrupting the field in response to a control signal corresponding to the time for a mark. The interruption is synchronized to alternations of the field and movement of the wireline. The interruption begins between alternations of the field and is maintained for a time sufficient for a predetermined length of the wireline to be moved beyond the application zone. This predetermined length is related to the length of the zone on the wireline affected by the alternating magnetic field, which is applied with a U-shaped electromagnet held in proximity to the wireline. Wireline movement pulses are generated by a tangentially coupled measuring wheel driving an encoder.