The calculation is done locally, in the browser, without sending the data to a server.
The precode must be composed of a letter followed by 3 numbers (example : A123).
The precode is written on the back of the car radio. On radios with physical buttons it can be recovered without removing it by simultaneously pressing the keys 1 and 6 (or 1 and 5) and the power button. The code generator does not work for precodes starting with A0.