Well, it's pretty simple, but most people don't have the tools or measuring equipment to get the numbers.

Firing pin travel to the boltface, which is total travel, minus firing pin protrusion. (for example) .285" total travel......minus .035" protrusion, = .250"
Net spring force, which is force at full cock, minus sear drag. (for example) cocked 23.5 lb....minus sear drag of 4.2 lbs = 19.3
.250 x 19.3 = 4.825