Replacing the dashboard?

Could you tell me: What is the principle of the speedometer (electronic or cable needed) and the tachometer on the dashboard "Speedometer KOSO for GILERA".
How information is removed (which are detector and where it set)?                                                              I would like to put it on my "BWS 50" (1996).
Is it possible to convert it for my scooter?                                                                                                 Does anyone know?
Thank you.