Kees, TNT is not a sharpness test, and it should never be your first test, because it will dull a sharp edge.

Do your sharpness test when you first pick up a razor, whatever it is (HHT?). If your showing some grab, you shouldn't do the TNT, but just tone up the razor on an 8K (or do a conservative pyramid with a test in the middle). Even a razor that has just passed the TNT will show a decent amount of sharpness (grab on the thumb test).

I would only do the TNT on a razor after it shows a poor result in your sharpness test, whether the razor is previously sharp or new (Ebay). It may not need a lot of work.

Basically, you need the TNT to tell you why a razor is not sharp, if you can't seeit by inspection. If it passes the TNT, you know you're not far off, but you do need to hone it to keenness. You would not want to use a lot of 4K then.

If it doesn't pass, you'll know if the razor is dull, has a wire edge or an invisible chip (and where it is). These are all defects that require you to restore the edge (starting with the 4K), and the TNT tells you how to proceed (do you need to back hone or work out a chip on the 4K alone?, with circular strikes? or do you just need a pyramid- should it be aggressive or not?).

The idea is you know what each razor needs, and you're not jumping in blindly and doing a bunch of pyramids that put a close edge out of reach. A chip takes a lot longer to remove with pyramids than with circular strokes on the 4K. A wire edge will be fixed quicker with back honing than with a bunch of pyramids. You need to do what's right, not jump in blindly.

I'm not suggesting that any of this applies to you. I'm just explaining why , how and when to use the TNT. It and an inexpensive microscope will keep you on track.