I hadnt thought of that but love the idea, well done.
Over here we have door stops, that are screwed to the floor to stop the door banging in to the wall when opened, they vary in design but you can get them that are a disc of metal or plastic with hard rubber on top and a scerw hole through the middle,
Put a bolt through the hole and through the ruler with a nut on the end,
I suppose you can also use the scale on the ruler for differant pressures for differant locks, the longer an article is the more torque is applied so if you hold it at the end furthest away from the rubber stop you will get loads of spring in the ruler and it will hit the key hard, hold the ruler nearer the rubber and it will be harder to bend and not bend a sfar so should hit the key softer,
Perhaps thats just over the top and wouldnt work but again i do like your idea, well done
