Larry;
Go back & re-read R-man very slowly & carefully. You're not quoting what R-Man said at all. The Strain gauge does indeed only measure the pressure at one point. It is set at about the 1" point to be sure & catch the peak. Yes it only occurs once, that's exaxtly what R-Man said.
You are I think confusing these gauges with the action of a crusher which can only measure the (1) peak. The strain gauge on the other hand gives a continous reading of the pressure in the bbl. As the shot moves on down the bbl, the pressure falls (Decays) & it does so over the entire length from breech to wads at a basically even pressure. Thus while if a load peaks at 9K for instance 2" from the breech, this is the only pressure which a lead crusher will record, even though at the 6" point the pressure may be only 4K & will also have that amount of pressure now at the 2" point as well. The Strrain gauge on the other hand will record both the 9K & the 4K pressures & give the "Time" they occured.
Bell could have gotten very accepctable results with the use of only one gauge. He could of course have simply read the Cox/DuPont results which had been on record since the early 1920's & had adequantly proven & recorded what he was trying to determine. These tests were I believe done using Piezo Electric gauges which were also capable of reading continous pressure curves.
If you will just go back & comprehend R-Mans posts you will see they are not contradictary at all but straight forward & quite easy to understand. The absolute "Peak" pressure was of course reached only once. The "Peak" at any point beyond did not reach the same pressure as that high point of the entire bbl, but was the peak for "That Point". Thus from my above scenario the bbl peak would have been reached at 2" @ 9K, but the peak at 6" was 4K, the pressure never reached 9K @ 6" from the breech. A strain gauge set at the 1" point would have shown a reading of 9K when at the 2" peak & 4k when the wad passed the 6" point as the pressure would have been equalizing all along the bore as the shot traveled down it. The pressure did not stay at 9k at the peak point for the entire time the shot was in the bbl.
If you put a pressure gauge on the valve stem of a tire & it reads 32psi, & you then go half way around the tire & stick an ice pick in & yank it out as you hear that hissing sound the pressure will start to drop at the valve the same as it does next to the puncture, it'll go flat all the way around. The one gauge will read the pressure in the entire tire, just as that one strain gauge will read the pressure in the entire bbl.
