Just like Grizzlypeg says, I'd measure the distance from front to rear sight and the height of each notch on the elevation ramp. The only difference in my approach is that I use ratios, so at say 20" of sight radius and one step is .09", I would take the target distance in yards (say 25 yards), convert it to inches (25 yards x 36), divide it by the sight radius, then multiply by the notch height. That would tell you what a notch is worth at 25 yards, but if 100 yards was used for the target distance, then you'd have basically MOA.
Results in my example would be 25 x 36 / 20 x 0.09 = 4.05" per notch at 25 yards. That would be approximately 16.2 MOA which is a lot, but I just picked numbers off the top of my head here lol
I use this strategy to figure out adjustment values on my open sight guns. Sometimes I'm figuring out the increments by thread count on a aperture post. On a ramp like Williams and Remington rear sights have I measure the ramp height at the first and last lines, find the difference and divide that by the number of lines to get the value of height change at each line... There's always a way to figure it out with a caliper and calculator.