Dial-Indicator - Meetklok
We have several dial indicators in the metal woodshop. Consult http://www.mini-lathe.com/Measurement/Dial_indicators/Dial_indicators.htm or youtube for countless videos on how to use them. Or ask someone to show you.
I've you've never used these before (or are in doubt which one to use) then use the one in the big red box. It is the easiest and most versatile.
Red-armDirk-Willem van Gulik.
The thread on the M6 bolt holding the indicator on the arm (lower left in first picture) was gone. TIG-welded extra metal onto the damaged thread, ground/turned it to 6mm, re-cut M6 thread (20191226, AlexY)