A 10" Troughton & Simms Pattern Level is shown in their 1897 catalog (see picture) has the same features as this instrument so it was likely made in the late 1800's. But as indicated below dating is inexact because they did not place serial numbers on their products.

From Microsoft Co-Pilot: "The Troughton & Simms Pattern Level was a high-quality surveying instrument available in 10-inch, 12-inch, 14-inch, and 16-inch models. These levels were supplied with either three screws or four screws, depending on the user's preference. The four-screw design provided greater stability and precision, making it ideal for high-accuracy surveying tasks. According to historical catalogs, these levels were often equipped with parallel plates, allowing for fine adjustments in leveling. Some models also included a compass, enhancing their functionality for fieldwork."

Troughton & Simms began in business in London in 1826. Its origins in the instrument-making business begun in 1764 by John Troughton (1716-1788). This business was successively passed down first to nephews, John Troughton (1739-1807) and then to Edward Troughton (1756-1835). In 1826 Edward Troughton took on William Simms (1793-1860), who worked for him as an apprentice, as partner, Simms 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. When William Simms died in 1860 the company was next managed by his son William Simms (junior) and his cousin James who carried the firm into the industrial age.

The 20th century brought important changes to Troughton & Simms. The firm became Troughton & Simms, Ltd. in 1916 after James Simms died. 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.

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".

Above history from: https://amhistory.si.edu/surveying/maker.cfm?makerid=33", https://en.wikipedia.org/wiki/Troughton_%26_Simms and  https://collections.qm.qld.gov.au/persons/16714/troughton-simms