An antique brass circular protractor, made be Troughton & Simms of London. This brass protractor is engraved with the maker's name. Measuring 6 inches in diameter is in fine original condition and is circa 1826.
Troughton & Simms was a British instrument-making firm, formed when Edward Troughton in his old age took on William Simms as a partner in 1826.  Edward Troughton died in 1835. Troughton & Simms's shop in Fleet Street became the hub of the finest scientific instrument making in London, in a period in which there was an expanding demand for precision instruments for astronomy, surveying and precision measurement. They made instruments for Greenwich Observatory, for imperial surveys and exploring expeditions. 
Note the early features: The single numbering of degrees, instead of double numbering in reverse directions, and the decorative five-degree divisions, divided to half a degree.
On verso. S.G.O. No. 70.
The instrument is a nice example by an important maker.