I learned to use a Stadimeter in 1969. I picked this one up in 1976, at the Navy salvage yard in San Diego. A stadimeter is a piece of technology that was used for many years, to determine the distance between ships when steaming in formation. We didn’t use it much in the 1970s, but we knew how to use it, in case our other newer, electronic technology was not right, or appropriate for the specific tactical situation.
The newest technology is not always the best technology for the situation. Angles, mirrors, knowing height of eye…all useful in determining the distance between your position and the other ships in the formation, without giving an electronic footprint (and other reasons perhaps).