Touch business card until you can feel it. Set display to the thickness.
The for really accurate, with cutter spinning, and observing with high magnification bring it down until you can see the cut, just.
or
With spindle stopped. This takes longer to type than do. Doing it is under 10 seconds.
For cutters as small as 1mm, on my SX3, which has a quill (couldn't live without it) I just move down near the job with CNC control, then UP a tad to cancel head nod.
Head nod on the SX3, (going up makes it go down a bit on the change of direction due to slide friction) makes the CNC UP step above important.
Bring the quill down until I can feel it touch, and then a little more so the backlash in quill handle is overcome.
This means the return spring on quill handle is not interfering. Now I lock the quill, and zero the DTI (I have a mechanical one), and zero the CNC DRO. (touch screen)
Mover the quill back so DTI reads zero. My DTI has 1 micron steps!!.
I can set to better than 2 microns, on production basis doing this. Then it is back to my wife who operates the cycle start button.