(11-02-2016, 06:46 PM)knockknock Wrote: I don't know if this was ever made, but your plumb bob is real close:

http://www.google.com/patents/US2713211

2 Claims. (Cl. 33-216) This invention relates to a centering device particularly adapted for use in combination with the frame or chassis of a motor vehicle, and in particular a weight in the form of a plumb-bob having a pulley block on the upper end and a point extended from the lower end whereby with the pulley positioned to travel on a cord suspended with slack therein between two points the weight of the device will cause the pulley to travel to a point substantially midway between the two points from which the cord is suspended.