I needed a DRO (digital read-out) on the tailstock quill of my Colchester 1800 lathe. OK, the quill has an engraved mm scale and the wheel on the leadscrew is calibrated in mm, with 2.5mm per turn in multiples of 100 micrometres. Still a pain when you need to drill a hole 52.95mm deep. After watching a couple of Youtube vids, I saw a neat solution by ChrisB257. Make a collar to be a very close fit to the end of the quill, split it and put in some clamp screws, then fix a right-angled tab which can be used to attach the magnet on the end of a sliding electronic digital scale.
So, part 1 is just the quill clamp collar and magnetic tab. Collar is turned from 70mm EN3 steel round bar. Tab is from an offcut of EN8 I found in the scrap bin.