Stuart's Distance Metre

Today I felt reasonably fit and decided to do some tidying up.  I succeeded in getting most of what I intended to do, done, before I moved awkwardly, trapped the nerve in my back and had to stop.  I rested for a while until the painkillers etc., started to work and then decided to sort through my instrument collection.  I was delighted to find that the dust and dirt from the building work had not managed to penetrate into the cupboard, which I sorted through fairly carefully.  During this activity I came across my twenty-six year old Stuart’s Distance Metre.  This was originally designed for marine use, where a distant object is looked at through a telescope via two opposing prisms and a control is adjusted until the top of one image becomes co-incident with the bottom of the other.  Assuming that the height of the object is known, at this stage it is just a matter of reading off the multiplication factor scale and multiplying the height of the object by this to get the distance. 
 
I could not resist having a play with this instrument, which carries a scale plate manufactured by me in my little workshop, so that this instrument no longer reads in cables, but gives a direct ratio.  I checked it out against a modern laser distance metre, and although not the same results, there was never an error of greater than about 2%.  Satisfied with this, I put the instrument away again, but before doing so got a couple of pictures of it in my hand, hence today’s blip and my extra picture.