They are basic dial indicators with magnetic bases, trueing stands normally do not come with dial indicators although Park does offer them as an extra. Mine read in 1/1000 increments with my happy place being between 5-10 thousandths for new builds while used wheels might never get that close.

Consider that I build wheels as a profession and that neither my partner or I has a commercial stand save for my old Hozan which is a commercial grade stand used for factory building.

Made a little movie... shows the gauge at work on a wheel that had seen a good 5000 km of hard use which was still within 6/1000. It can also be used to dish wheels as you can get a very accurate read on the lateral position of the rim and make accurate adjustments without needed a separate handheld gauge which is not as accurate and more time consuming to use. As the lateral gauge is fixed to the stand it does not move out of place while the vertical gauge can be moved about.

Wheel Trueing

You can see I still use zip ties... I also affix these to my bicycles and just leave them there in case I have to do any on the road servicing and they serve as little warning indicators as if a rim goes off it's alignment they start making noise.