Most piano actions can be made to play smoothly and evenly.
In the photo below, new hammer shank flanges are being measured for resistance. The new flanges varied from 2 grams to 5 grams. Once measured, all flange bushings are reamed and repinned for 3 grams of resistance. This gives the artist a smooth and even playing action.
Note the new hammers in the background and the 500 gram scale. The hammers are glued on the flanges and then individually weighed to tenths (0.20) of a gram. The weight on Note #1 can be 10.5 grams and note #88 can as little as 3.5 grams. Using a graphed chart, the hammer weight is kept on a smooth curve resulting in an piano action that plays beautifully.
Using gram weights to weigh off the keyboard.
Once the hammers and flanges are weighed, the action is then assembled and regulated to the piano. Then the keys are weighted for even playing. A current Steinway Model B is generally weighed off to these parameters:
#1-16 (51 grams) of Downweight (DW) Upweight (UW) +20 grams
#17-32 (50 grams)
#33-45 (49 grams)
#46-61 (48 grams)
#62-75 (47 grams)
#76-88 (46 grams)
Note that the above figures vary instrument to instrument and concert instruments can be weighed off to as much as 55-58 grams of downweight (DW).