Bill headings commonly depicted trade signs in the 18^th century. Henry Gregory (fl. 1750-76) was clearly a scientific-instrument maker (or seller) from the context of the sign, although his trade is not stated.

The principal interest of this engraving is that it shows a composite sign, partly painted, partly three-dimensional, together with its bracket. Henry Gregory’s azimuth compass, with its distinguishing ‘hypothenusal lute string’ is depicted alongside a three-dimensional Hadley’s quadrant, which Henry Gregory added to his bill heading in 1761, thirty years after its invention. An azimuth is ‘an arc of the heavens extending from the zenith to the horizon which it cuts at right angles’ (OED). An azimuth compass was ‘a minutely divided mariner’s compass fitted with vertical sights, used for taking the magnetic azimuth of a heavenly body’ (OED).