Make the Wally Skater yourself
Construction drawing of the skater meter
Necessities:1) Lineal with inch graduation
2) Aluminum tube 10 mm. and 6 mm
3) Plastic or wooden base plate
4) Some sewing thread or fine fishing thread
5) Plumb bob
Cut the aluminum tubes to size
The 10 mm tube will have a slot for the ruler and a 6 mm hole for the top guide.
I turned a ring on the top guide to attach the wire. But of course you can also come up with something else, as long as you can slide it.