You now need to rummage through your tool box and find two items – one that weighs 51g and the other that weighs 510g. Attach these items to a bit of wire or string and hang them at the 10cm point on the balance tool.
Position the balance tool on the end of the input shaft and make sure that this connection does not slip.
I wrapped a piece of masking tape around the splines of the shaft and drew a mark on the tape and the balance tool so that if the joint moved I could easily see any misalignment.
Hang a weight on one side at the 10cm mark and then move the same weight to the other side of the balance tool so that you get an idea that the force you are applying is resulting in the same response on either side.
Example:-
You can now work out the force required to turn the shaft. Say for example the shaft is loose enough that at 10cm the 510g weight just falls off – the balance tool spins from the horizontal position towards the vertical and the weight falls off. You can now reset the balance tool to the horizontal position and re-hang the weight at say the 5cm point. Say for example this time the balance tool moves slowly from the horizontal position until the weight eventually slides down and falls off.
However when you reset the balance tool to the horizontal position and put the weight at the 2cm point the balance tool stays level. You find that placing the weight at the 2cm point on the other side of the balance tool also results in the same – the balance tool stays level. So using the equations above you can “backwards calculate” the torque that you are applying.
And because we're hanging the weights at the 2cm point (instead of the 10cm point)
You can see that by applying a different weight at a fixed point or moving a weight along the length of the balance tool you can adjust the applied torque to a value that you require.
The trick is to position the weights on the balance tool so that it “just doesn't” move.
You could use this same method for setting up the pre-load torque on a W123 / W126 differential input shaft – so it is worth remembering.