Functioning of the instrumented cylinder and experimental set-up used for its calibration. The apparatus is designed to measure the orientation (θ) and vertical location (x) of the applied force (P) by either the index or thumb while exerting a grip force (in A and B). These parameters are calculated from outputs of an F/T sensor (with axes X, Y and Z) embedded in the two half-cylinders using two T-adaptors (upper panel of A and C; T-adaptors indicated in hatched, the F/T sensor in black). In order to verify the accuracy of measurements, the cylinder was mounted on an angular positioning tool by clipping one of its ends, aligned horizontally, on a milling table (not illustrated) and we used a linear positioning plate (2 upper panels of C), in order to apply five different masses (P in 2 upper panels of C: 100, 200, 300, 400 and 500 g) vertically on each point of the matrices formed by the nine angles (-80° to +80°) and nine heights (10 to 90 mm) and indicated by the dashed lines. The sensitive side of the transducer is the one linked to the half-cylinder with only the T-adaptor inside it and not the body of the transducer (in black) itself (upper panels of A and C).