The invention concerns a clamping device comprising a tensioning spindle whereof one end has a first axially fixed support surface and whereof the other end has a second axially mobile support surface and mobile relative to the first support surface through a clamping element. The change-gear mechanism has an input shaft, an output shaft and an actuator for changing a change-gear ratio between the input and output shafts. The metal wiring is connected to the bend via at least two contact holes formed in the insulating layer. The coordinate calculator calculates a unconverted coordinate used to calculate a converted pixel value located at the converted coordinate.