STOP! The thumb should never be moved along the edge unless you're trying to reduce its size.

The thumb is oved across the edge. A dull blade will permit it to slide across, while a keen one will grab the thumb and move with it.

The thumb tilting can be done by simply bending the thumb. I added it to weed out the butterknives. It's not part of the traditional thumbnail test.

You can find a thorough description of both tests and what the different results mean at classicshaving.com, in the "how to ... and why" section where honing and stropping are described.

Traditionally, the thumbnail test is done while you're honing to form the edge. It tells you when to leave the hone and begin stropping. The thumb test is then performed as you hone to determine when the razor is sharp enough. This assumes that you use one hone and a leather strop.

I modified the tests and combined them into a system. Prof. Vanderhoeven found that leather stropping after honing has little effect. I found that other than smoothing the edge, it does very little, but a litle smoothing doesn't hurt.

My approach is that when I pick up the razor, I do a thumb test, and I'll touch up if the razor is reasonably sharp. If it fails, I go to the thumbnail test to determine what I need to do.

If you're forming a new edge, you come off the 4K when the razor passes the thumbnail test. That test has several ways to fail, and each negative result indicates a different problem (see classicshaving.com for details).

When you come off the 4K, the blade will already do reasonably well on the thumb test. The idea is to get it keen. I'll work the blade on the 8K and test frequently. You can feel the grab increase, and you can feel an edge forming and getting thinner. When I see little improvemnt in successive test, I move on to the next finer grit and do the same, and I'll continue that way until I finish the finest abrasive. When you pass the thumb test on the 8K (no further improvement), the edge may already be keen. If so (or if you've finished your finest grit), move to the leather strop and do about 15 round trips to smooth the edge.