<p>The device has a sole plate (2) with two bearing surfaces that are selectively positioned and aligned with one another. Two clamping pads (31, 32) are utilized for receiving knees of an operator. The pads are projected with respect to the sole plate and integrated with the respective bearing surface. Each of the clamping pads comprises a shell formed of foam of synthetic material. Each shell comprises a recess filled with gel. A set of holding devices i.e. magnets, holds the bearing surfaces in respective positions.</p>
