Rangefinders measure the slant (line-of-sight) distance. For elevation holdover, what matters is the true horizontal distance.
Method: horizontal = slant distance × cos(angle) — the "Rifleman's Rule" cosine correction for scope holdover at a shot angle. Sign of the angle doesn't matter.
A target's angular size in the scope depends on both its real size and how far away it is. Solve for whichever one you don't already know.
Method: size = angle(rad) × distance — the linear approximation reticles are calibrated with. Settle the horizontal stadia line on the base of a known-size target, read how many mrad/MOA it covers up to the top, and that gives you the range.
Milliradian — 1/1000 of a radian, metric and linear. The standard for holdover and ranging on European/tactical scopes, and what most Finnish shooters dial and hold in.
Minute of angle — 1/60 of a degree, imperial tradition. In Finland it mostly shows up describing group size, rarely on the turrets themselves.