Ny initial estimate for probe spacing was 1/2 cm, and that was a guess. Initially, I was considering a longitudinal track with nominally 100 probes spaced at 1/2 cm because it could cover the length of a relatively long stump, where half-a-meter was not particularly unreasonable, though most would probably be shorter. Presently, I'm persuaded that a circumferential arrangement would work well, too. half a meter is not completely unreasonable for maximal circumference of a large stump, though the justification for 50 cm is that it has to be substantially larger than what is likely to be encountered. A half meter is on the order of twenty inches, and my own knee is about 17 inches in curcumference. I don't think it unreasonable to consider that someone, somewhere might be that much larger than I am.

Keep in mind, please, that adding another degree of freedom to the movement of the apparatus increases the cost and complexity considerably.

RE