Abstract: The invention relates to magnetic recording. A method of superposing a modifiable magnetic code on a fixed bar code magnetizes the bars in two different directions by means of a write head. There is the provision for synchronising the application of write signals to the write head with the passage of the bars of the bar code and the system may include a bar code reading head which reads a code moved by a conveyor belt and which causes an image of the bar code to be stored in a shift register with each bar and each space of the bar code being represented by several successive 1's or 0's. The write head then includes a read winding which triggers (via) reading of the image, and the image is gated into a code generator that writes when an image bar is present thereby writing magnetically onto the real bars of the bar code.