The cavitometer is a unique tool allowing a direct measurement of the sliding velocity at the base of the glacier. It is simply composed of a bicycle wheel attached to a 1.30 m long articulated arm that is fixed to the rock and placed in a natural cavity, free of water, that opens behind a bedrock bump. Sliding velocity are measured at an hourly scale from this subglacial laboratory since 2017 thanks to a new potentiometer and a new numerical logger. Daily sliding velocities were measured almost continuously since 1997. Luc Moreau is in charge of this measurement.