I wanted to know what the seat pressures of some NOS '56 springs were going to be at an installed height of 1.780 in. The tester tool came from ebay, costing very little. The exact same tool is pictured in one of my old Motors books.A torque wrench is used to measure pressure. The wrench's reading is then multiplied by 2 for the spring pressure. I set the tool to stop at 1.780 using a snap gauge set at the same measurement. Gradually worked to the correct torque setting, then checked it by going plus and minus 1 and 2 lbs. The final result was 39 lbs., times 2, for a spring pressure of 78.
Took the spring to a friend's for verification on his Remac tester, and he measured it to be 80 lbs. Good enough for government work!