Good answer Joe!
Here’s a couple of points to be aware of:
The socket-head cap screws that came with my VSTAs tended to skew the angle of the VSTA when I tightened it. The answer was to grind or file flat the end of the screw.
When setting the position of the VSTA, hold it flat against the stone you’ve just set the angle on. Also try to hold it perpendicular to the angle bar. When you are satisfied with the position, tighten the VSTA screw. In the photo below, you’ll see that like Joe, I placed a sheet of paper under it to make it easier to see what I was doing. I used the paper only for photo purposes.
https://tcmeyer.smugmug.com/Wicked-Edge-Related-Stuff/Wicked-Edge-VSTA-photos/i-G3kHvmC
It’s important to note that once you’ve set the VSTA, it becomes your angle reference. All stones - even the stone you just set the angle on, must be reset to the VSTA. This is because of any errors that might have occurred when tightening the VSTA screws. Again, all stones should be set to this reference.
The objective here is to make the rod exactly parallel to the face of the VSTA. In the photo below, I show my technique in setting the stones against the VSTA. I tightly pinch the rod against the bore of the handle with my thumb on the back of the VSTA bar. Then I adjust the stone toward the VSTA until I feel it bottom out. If the end of the stone nearest you is already touching the VSTA, back off on the angle (using collar or microadjusts) until you see daylight between the stone and the face of the VSTA (shown in the photo), then adjust it toward the VSTA until you feel it bottom out. The adjustment you’ve just made puts the rod parallel to the bore. If the bore is parallel to the face of the stone, then the rod is also parallel to the VSTA.
https://tcmeyer.smugmug.com/Wicked-Edge-Related-Stuff/Wicked-Edge-VSTA-photos/i-JTKgfRN
You’ll want to settle on the amount of force you apply when bottoming-out the microadjusts, trying always to apply the same amount of force. Apply too much force and you can feel the rod being forced out of parallel. Once you’ve got the sequence figured out, it only takes about 5 seconds to set your stone angle to the VSTA reference. A few years ago, I did a sequence of tests and found that the variability in the angle after adjusting to the VSTA was only about 0.1 degrees. I’ll have to repeat those tests now that I have an angle cube that’s twice as accurate.
If you have stones which differ in thickness by more than the range of the microadjusts, you may want to modify your collar setup. Some of us have flipped our angle bar, putting the detents on the back side. Then we added a quick locking lever on the near side. This lets you make rapid adjustments without having to deal with the detents. Loosen the clamping lever, slide the angle collar to where the stone is flat against the VSTA, then reclamp. Now you can use the microadjusts as described above. If you want to use the detents for multiple facets (convex edges?) you can still do so with the screw on the back side.