Fig 2Key balance and touch weightClick a weight or a lead · 1–5 · L0 g on the key · goes down at 47.1 g
The last weight placed, and the dial's needleKey, leads and the 190 g action load on the capstanBrass weights: 20, 20, 10, 5 and 2 gWeights on a key's front, 13 mm from its edge, press against the action's weight on the capstan, here a 190 g brass load as a stand-in. The key balances at 34.6 g with both leads in. Friction in the bushings, the balance hole and the capstan adds about 12.5 g in whichever direction the key moves. So it only goes down at 47.1 g (the downweight) and, once down, only comes back up when the load falls below 22.1 g (the upweight). Each lead is 31.6 g of lead. Taking the front one out raises the downweight to 73.1 g, which is how a technician makes a key heavier or lighter. The dial reads 0.01 mm per division, one turn per millimetre.