Troughton & Simms began in business in London in 1826. Edward Troughton (1756-1835) had learned the trade from his father, John Troughton, a leading instrument maker in London; he also worked with his equally talented brother, also named John. William Simms (1793-1860) had a less distinguished pedigree, but proved to be an excellent craftsman and businessman. Under his leadership, Troughton& Simms manufactured mathematical instruments both large and small, and attracted customers around the world.

The 20th century brought important changes to Troughton & Simms. The firm became Troughton & Simms, Ltd. in 1916. A 1922 merger with T. Cooke & Sons, Ltd. led to the formation of Cooke, Troughton & Simms. This, in turn, became Vickers Instruments, Ltd, in business from 1963 to 1988.

From: https://en.wikipedia.org/wiki/Troughton_%26_Simms

Troughton & Simms did not normally place serial numbers on their products, so dating them is inexact. The "Troughton & Simms" name was originally engraved in copperplate, which later changed to a much simpler font. In 1915 James Simms died and the business passed to his sons. They made the company into a limited liability company. After 1915, the company name found on their products is "Troughton & Simms Ltd". After the First World War, business and long-term prospects were poor, and in 1922 Troughton & Simms was bought by T. Cooke & Sons of New York to become Cooke, Troughton & Simms.

Notable instruments from this period include a typical late 6-inch theodolite for use by engineers and surveyors and a typical late surveyors level, which can be dated to before 1915 by the lack of "Ltd" after "Troughton & Simms".