binocular range markings...???

D= is the Distance to the object in meters.
OH = is the known Object Height.
M= is the angular height of the object in number of Mil. THis refers to the number of lines /range lines/Mill lines the target fills.

D=OH/MIL x1000

Normallyyou have to guess at the height of the target. example if looking at a human I use a height of six feet.

With the typical 5 mil scale (each mark is 5 mil), a lighthouse that is 3 marks high that is known to be 120 meters tall is 8000 meters distance.

8000m=120/15