Kinematic key and hammer data for all the studied keys, obtained from all considered excitations using the mechanical arm, under controlled conditions of inertia and excitation force (M = M_I and 0 < F < F_I, see Tab. 1). (a) Increment in the key squared velocity, $V_{\mathrm{On}}^2-V_{\mathrm{Off}}^2$, between 10% and 90% of its displacement during the acceleration phase, as a function of the average acceleration 〈A〉 in the same time window. (b) Maximum Hammer Velocity (MHV), as a function of key velocity at MHV time. The dashed lines indicate the average slope of the data for each piano, estimated by robust linear regression and constrained to pass through the origin.