Originally Posted by
Jimbo
I always think of a test in two ways: 1. What is it's purpose?; 2. What's its fidelity to reality?
From the purpose perspective, in my opinion the purpose of the HHT is to give honers an idea of where the edge is before they test shave it. From that point of view it's not really something a user of a straight should care about but of course we all do :) It's a weird test because you can get a successful HHT on an edge that really shouldn't be shaving anyone as well as on a "good" edge. You can also get an unsuccessful HHT on a "good" edge. So you really need to know other bits of information for the HHT to be useful, and that information is often unknown to the end user but is known to the honer.
Second, fidelity to reality is quite important for any model-based test which is exactly what the HHT is. You don't shave by wafting your hair over the edge of the razor. Your beard whiskers are not head hairs, or dog hairs, or your wife's hairs etc. Your beard hairs are shortish, coarseish, and most importantly embedded in your skin. When you shave the edge rests on that skin. Is this even remotely modelled accurately by holding a hair in the air and seeing if it gets cut on a stationary blade edge? I don't think so, but others may disagree.
The only way such a divergent-from-reality test can even remotely hope to help you understand if an edge can shave you is by repeatedly, over time, noting the test results and correlating (not the best word, but will do) that result to what happens during the corresponding shave. That is the only way.
So really, the HHT test has two parts, and people either forget or ignore or don't know about the second and most important part. First you waft the hair over the edge (this is the bit people mistakenly think is the HHT). Second, and this is the most important part of the HHT, you test shave it and relate the results of the first part to the results of the second part.
Do this test several hundred independent times under varying conditions to get a decent sample size. Then you are in a position to know what the HHT is telling you.
James.