Archibald Barr and William Stroud, professors of engineering and physics respectively at the University of Leeds in the 1880s developed the prototype of this optical rangefinder in response to a competition from the War Office. The instrument was adopted, first by the Navy and then the Army, and was widely used during WW1.Meanwhile Barr and Stroud had resigned their posts at Leeds to set up the company, Barr and Stroud, optical instrument makers – a company in Glasgow.
After the war, instruments with military applications continued to be developed and produced by the company, such as in 1930 they were awarded a contract to supply binoculars to the Royal Navy. They also diversified production into instruments for civil use, particularly aerial and topographic survey..
The model shown here, the FT 27 with a 0.8m base, was used by the infantry in WW1 and 2.
I've tested this instrument and it is still fully functional. The last 3 pictures are with the original
No 14 MKIII stand.