NavList:

Hi David,

There is more than one problem with the video - which is why I described it as "for a general audience".  I should have been more precise and less "black humour" given that the written word is not good at conveying sarcasm.  The benefit of the video is that it provides a good close-up view of the instrument.

The video describes the concept of the triangle, but gives the impression that the base of the triangle is the instrument itself (it talks about "two telescopes").  Of course the base of the triangle is defined by the extremes of the object being viewed, and the instrument is, for all significant purposes, a single point at the apex.  

The laser does nothing but show way the the mirrors work for a viewer through the telescope.  You are of course correct that the light used for the measurement is coming "into" and not "out" of the instrument.

As for RAS - in the pre-electronic era - I don't believe that the instrument was used as an aid to holding station once the two ships were in physical contact - i.e. once the  gunline (the light line that is sent first between ships) is in place.  My understanding is that it was used during the approach of the ship to be refueled to the refueling tanker (or any other for of RFA - not just fuel).  Once the two ships were together, a distance line was used.  This was the first line to go across after the gun line - being attached to the first point on the messenger line (which was pulled across with the gun line).  The distance line was taken forward on both ships and was marked with flags at known distances.  It was a visual tool to allow the receiving ship to hold station.

There are several videos online that demonstrate this - but of interest to the current discussion are two things.  On older videos and photographs which feature the approach of the receiving ship to the supply ship, you can sometimes see a figure on the bridge holding what appears to be a sextant - distinguished from those with binoculars by the way it is held.  My guess is that the object is a stadimeter.  Secondly, there is a good video of a modern RAS - search YouTube for Operation Atalanta RAS.  As the receiving ship approaches the supply ship from astern there is a good view of a sailor using a modern handheld laser rangefinder directed at the supply ship  - the same type of thing we might use when playing golf or perhaps hunting.