I made a fixture that puts the forestay on a lever with the other end of the lever on a scale. The lever is attached to the stem fitting. The lever has a 10:1 advantage. As I tighten the backstay, I can read tension off the scale and off the PT-2 gauge. The scale shows that the tension increases very linearly with backstay turns. This is what Hooke's law says should happen so that is good. The PT-2 gauge reads a non-linear sharp increase in tension as the backstay is tightened. My scale reading is very close to a PT-3 reading by the way.
Now the interesting part. I had my PT-2 calibrated by Loos and it was accurate at a reading of 38, which is 1300 pounds but my scale reading says 1150, and the PT-3 says 1075 pounds.
The only difference I know of is that they used 304 1x19 and I have 316 1x19. Could that make a difference in the reading on a PT-2 but not on a PT-3?
My writeup is here:
http://l-36.com/loosaccuracy.php
Allen