Abstract: A system for reading and encoding a magnetic track (2) carried by a supporting document (1) which is displaced manually past read and write members, the magnetic track comprising a first portion (3) on which a fixed first encoded message characteristic of the supporting document is recorded, said message being encoded by means of an encoding system which conveys its own clock signal, the first portion of the track being followed by a second portion (6) in which a variable second encoded message is written each time the supporting document goes past said read and write members, wherein the read and write members comprise three magnetic heads in alignment, comprising a first head (9) which is a read head, a second head (10) which is a write head, and a third head (11) which is a read head, the write head (10) being connected to a write signal generator (12) having a first input (13) which receives data representative of said variable message to be recorded on said second portion of the magnetic track, and a sec