Often using a dial indicator. A rack and pinion converts the linear to rotary motion, and gears magnify the rotary motion: https://en.wikipedia.org/wiki/Indica

Often using a dial indicator. A rack and pinion converts the linear to rotary motion, and gears magnify the rotary motion: https://en.wikipedia.org/wiki/Indicator_(distance_amplifying_instrument) https://en.wikipedia.org/wiki/Indicator_(distance_amplifying... tubalcain has a good video showing how they work: https://www.youtube.com/watch?v=Rp6D3YTx7iU https://www.youtube.com/watch?v=Rp6D3YTx7iU