Sector, by Thomas Heath, London, c. 1730

Brass sector on 12 inch radius and with extensive decoration.

The layout of scales is not identical to those on the other numbered Heath sector (inv. 49772); the pattern is closer to sectors by Culpeper (inv. 50251 for example). On the signature side is a mixture of sequential and symmetrical sectoral scales. The sequential scales are chords Cho (0-60) and equal parts Lin (0-10). Arranged symmetrically between them are secants Sec (10-75) and over the gap between the two legs on this side is a sectoral line of polygons POL (12-6). Against the edges are continuous scales for use with the sector fully opened: artificial tangents Tan (-45), artificial versed sines V. Sin (168-0), artificial sines Sin (-90) and a double scale of artificial numbers (logarithms) Num repeating just before the hinge.

The scales on the reverse also include a mixed arrangement of sequential and symmetrical sectoral scales.Sequential are sines Sin (0-90) and tangents Tan (0-45). In between are symmetrical tangents tan (45-75). There are two pairs of natural scales: inclination of meridian In-Mer (0-90) and latitude Lat. (0-90), and chords Cho. (0-90) and Hour. (0-VI). The continuous scales for use with the sector fully opened are: inches (0-24) and equal parts (0-200).