If I get one of my hairs (which I gathered when I cut it) to be consistent at least at HHT 4 along the entire edge, then gives me a smooth shave, I dare to call it shave-ready. This indeed does not mean that it is an HHT4 for the next person. It might drop off silently, it might need a slight drag, whatever. But if it shaves me comfortably that is all I can rely on to make sure it will at least shave someone else.

The point is that it is a useful tool in indicating when I am done honing, which areas need special attention, etc. If it won't pass at least a HHT3 (my HHT3 with my specific hair and specific method) I know it won't shave well enough for me. With an HHT4 (all after stropping) I know it is keen enough to shave with. Whether it is a smooth, comfortable shave, I do not know but I am confident enough to try that out.

If I don't get a reading at all, I won't even bother with a shave. I will give it another good stropping, another HHT, and take it from there. Plus I usually test with at least two different hairs (from the same bunch).

I never tried to perform my HHT on an edge honed by someone else but then again no one has honed a razor for me apart from my two first ones which I don't use anymore and messed up anyway. I probably would check it, just to see. But really, if someone dares to call an edge honed by them shave-ready, I trust he/she knows what they're talking about and would shave with it first before even considering putting it to any hone. Or stropping.

All in all it is a very personal and relatively subjective honing tool.