What is bar sag in alignment?

gravitational force acting on an object

bar sag| Dial Indicators| Precision Shaft Alignment| rod sag. ... I'm referring to thebars that holds your rim dial indicator(s) when performing a precision shaft alignment. Bar sag also called rod sag needs to be compensated for, should it occur, otherwise you are introducing a measuring error.

Bar sag is the bending of the bar supporting the dial indicator.This has the potential to introduce error in the alignment readings.

Dial indicator bar sag describes a bending of the hardware used to support a dial indicator or other part which spans the coupling. The bending action occurs as a result of gravity and cannot be totally eliminated in almost all cases of alignment.