Sector, by Thomas Heath, London, c. 1740

Brass sector on 12 inch radius.

The layout of scales is not identical to those on the other numbered Heath sector (inv. 36704). On the signature side are pairs of sectoral scales arranged sequentially rather than symmetrically: sines Sin (0-90), tangents tan (45-75), tangents Tan (0-45), as well as continuous scales for use with the sector fully opened: equal parts (0-200), double scale of artificial numbers (logarithms) Num repeating at the hinge, artificial tangents Tan (-45).

The scales on the reverse also include pairs of sectoral scales arranged sequentially rather than symmetrically: chords Cho (0-60), secants Sec (10-75), equal parts Lin (0-10). Arranged over the gap between the two legs on this side is a sectoral line of polygons Poly (12-6). Individual natural scales on this side are arranged in pairs: Hours (0-VI) and latitude Lat: (0-90), and Chords (0-90) and inclination of meridian In Mer: (0-90). The continuous scales for use with the sector fully opened are: inches (0-24), artificial sines Sin (-90) and artificial versed sines V Sin (168-0).