Voir ici: Servo - Arduino Reference
Writes a value to the servo, controlling the shaft accordingly. On a standard servo, this will set the angle of the shaft (in degrees), moving the shaft to that orientation. On a continuous rotation servo, this will set the speed of the servo (with 0 being full-speed in one direction, 180 being full speed in the other, and a value near 90 being no movement).
Donc dans le cas d'un servo classique, la valeur donnée correspond à l'angle en degrés.