I knew about micro testing, but not the ultasonic. It causes me to wonder though, if we are entering same as with pressure testing, copper and lead crusher units, measured physical deformation against a scale, vs piezo strain gauge electronic method of psi or metric equiv...no direct correlation.

And since ultrasonic is obviously not attempting to dimple a sample under a known pressure, and then deformation measured against a scale, it will only be approximate to original method, and truly valid only in reference to other results obtained with same technology....just as with pressure measurments...only valid when relative to results obtained the same way.

As an fyi, zone hardening is a misnomer, applicable perhaps to Japanese method and layers of clay during hardening. But, generally, here, knives are fully hardened, and then selectively softened after temper, in handmade by using a torch, and in factory setting via induction heating, to anneal tang/ricasso area, and more selectively in handmade to soften back and tip, as well.

And still hoping someone with several M stamped blades can chime in as to whether the M appears to be part of same stamp as name and all unitized, or a separate stamp. Cannot even begin to guess, based on my sample of one.