Sector, by J. Sisson, London, c. 1730

Brass sector on 12 inch radius with part of original case.

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: artificial tangents Tan (-45), artificial sines Sin (-90) and slightly more than a double scale of artificial numbers (logarithms) Num (1-1-1-2.4, ie 1-10-100-240), which repeats before the hinge. There are also two natural scales of rhumbs Rum (0-8) and longitude Lon (60-0).

The scales on the reverse also include pairs of sectoral scales arranged sequentially rather than symmetrically: equal parts Lin (0-10), secants sec (0-75), and chords Cho (0-60). Arranged over the gap between the two legs on this side is a sectoral line of polygons POL (12-4). Individual natural scales on this side are arranged in groups of three: inclination of meridian In. Me. (0-90), chords Cho. (0-90) and sines Sin. (0-90); and tangents Tan (0-45), latitude Lat. (0-90) and hours hou. (0-VI). There is just one continuous scale for use with the sector fully opened are: inches (0-24). Adjacent to it on each leg are two different scales: one is equal parts (0-100), the other is marked C (0-180).