Above is a top view of the Clearaudio protractor fully assembled.
Caliper measurement indicates that spindle hole center and null point have the same distance from the lower edge in this view. Note, that the spindle hole in this bottom plate is larger in dia. by .005 than the hole in the tower body meaning that this hole is meant to offer clearance and the tower body hole is intended to engage the actual spindle. In this view a caliper measurement from calculated hole center to null point reads 66.3mm (2.6125 inches) . Countersinks on opposite side will locate the bottom plate to the tower body.
Above view shows the spindle hole in the tower. The hole is off center by .007 measuring from edge of body. The wall thickness reading at either side of the hole is .050 inches knob side and .043 opposite.
On the other end is the trammel bar slot. The slot is centered to the body within .001. Running clearance between trammel bar and the slot it fits to is .004.
The off center spindle hole could be intentional or it could be a deviation from nominal during the production run.