[1][2] On 4 November 1766, at the approximate age of fifteen, William Spencer signed a seven-year contract of indenture (pictured) to Richard Rust, "Citizen and Grocer" of London, England.

The contract indicated that his father Anthony Spencer was a shoemaker of the parish of Church Minshull in the County Palatine of Chester, now simply known as Cheshire.

In consideration of the sum of ten pounds paid by William's father, Richard Rust agreed to instruct his apprentice, as well as provide him with the necessities of life, including food, drink, clothing, and lodging.

"[1] The agreement also indicated that Richard Rust was responsible for paying a duty to the Stamp Office, usually within one month of the date of the contract.

[1] William Spencer's master Richard Rust was a well-known mathematical instrument maker who ran a busy shop on Tower Hill in London.

[9] The camel is incorporated into the coat of arms of the Worshipful Company of Grocers, which also includes two griffins holding a shield (pictured).

[11] Spencer, Browning & Rust was a successful company, given the large number of surviving nautical instruments.

[10] The firm manufactured a variety of navigational instruments, including octants, sextants, telescopes, and compasses, for both domestic and international markets.

Nautical instruments marked with the SBR logo are found in the museums of a number of countries.

[11] The firm continued as Smith, Browning & Rust, operated by relatives of the original partners, until 1840.