[Gino]

These reticle scales are the basic means for determining target range. On COD's periscopes, on L.P. (low-power) each scale mark represents 1-degree of optical angle. On H.P. the longer marks are 1-degree apart and each shorter mark is 1/4-degree. Knowing that at 1000 yards range, a length of 52.5 feet subtends an angle of 1-degree provides you with a means for converting known lengths to range. It would be tough to do all but the simple calculations in your head, but the Range Omnimeter
is one example of a quick tool for determining range using these reticle marks. If the attack officer knows the masthead height of a target and sets this value on the Omnimeter, he can then observe the relative optical height of the mast in terms of scale divisions and then read off the range to the target directly from the Omnimeter.

For example, if I know that a ship's masthead height is 70 feet and it appears to take up three reticle marks on the vertical scale with the scope set on H.P. then I can immediately read from the Omnimeter that the target's range must be 1860 yards.

The horizontal reticle scale can be used in the same way using a target's known waterline length and estimated angle on the bow. Or the two ideas can be used together to first find the range, then observe the apparent waterline length, and then read the angle on the bow directly from the Omnimeter.

Other example:


I guess someone's gonna build this one next...
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groetjes,