Here is a photo of the glaze micrometer being used to measure the glaze on a test tile and giving a reading of almost .0017, or seventeen thousandths of an inch.
You can see how the plunger rests in the pad of my finger - It's right up above the 25 on the gauge - I'm using pressure to hold the needle against the clay body as the shoe rests on the top of the glaze.
The knurled knob that you can see closer to my palm, is used to set where the needle is with respect to the background. As the needle wears down you have to make this adjustment.
I have had this thing apart to work on it and it is really a very nice machine. Nothing about it is cheaply done.