Binoculars with a built-in compass also may have a ranging reticle.
In the Helios Oceanmaster the reticle is as shown on the left. The vertical scale from 0 to 7 is actually 0 to 70 mils. The horizontal is 0 to 40 mils each side.
In the Century Seapro the vertical scale has the numbers 20 ; 40 and 60 and the line goes from 0 to 70 mils.
The horizontal scale goes from left to right, from 0 to 80 mils.
To calculate distance from an object with a known height, such as a light house,
1000 x Object size in m
Distance = ------------------------
Reticle Scale Reading
Example: When the object is 20 m high and the reticle scale reads 16, as on the left, 20 x 1000 divided by 16 = 1250 m.