This is kind of a different way to do it, Its not suggested but it is a quick and easy and "relatively" reliable way to do a arm pot. I've used this method on encoders and pots on arms and drivetrains, all you need is a little wheel a bit of apoxy to mount the wheel to the shaft of the pot and a rounded area of whatever your measuring.
A problem with this method however is you have to constantly adjust your pot, every match you have to set it to make sure it didn't move and recalibrate.
However if you need a creative solution and can't drill into the end of the shaft or create a special coupler this is a solution we've used in the past and does work, and works well within the 2 minute First matches.
http://picasaweb.google.com/DanRRich...04765271712450