This holds a cheapie harbor freight dial gauge on the MakerBot Thing-O-Matic Z platform to aid in leveling. Using this I was able to square the platform within 0.025 mm (0.001") - which is close enough for me.

1) Use Multiply Print 2
2) slide onto dial gauge with the flat sides down. Lower Z until it just touches and zero it to the lowest corner of the platform.
3) Mount on Z and jog/adjust platform until all 4 corners are square with the print head.