Dial Indicator

[Hopefuldave]

Also, a dial indicator (plunger type) is used for direct measurement - but the measurement has to be in line with the plunger - and gives a direct reading, a dial TEST indicator (finger type) is used  to indicate whether or not there's movement, and is only accurate on its dial with the finger at a precise angle to the movement. This isn't a problem for the normal uses (centring in the 4-jaw, aligning a vice with the mill's ways etc.) where you're looking for an absence of movement, but can fool you if you're looking for e.g. precisely offsetting a workpiece in a 4-jaw to cut an eccentric, or mapping a surface for scraping!

Dave H. (the other one)