G'Day Matty,
Heres a couple of images of my effort at a digital height gauge. Callipers, $20 from Aldi & a piece of scrap cast iron for the base. I did need to use a cobalt drill & straight cutting oil, to drill the Ø3 mm holes through the calliper jaws. I made a goose neck holder & silver soldered a piece of HSS to it for the scriber.
The base was relieved to allow it to sit on the plate without rocking.
Hope this helps,
Don.