Six inch bras sector, 1720-1753.
© Science Museum / Science & Society Picture Library
A sector, decorated on hinge and legs with floral patterns, made by Thomas Heath, London. Sectors were used from the end of the 16th century until the mid 19th century to perform calculations involving proportion. The arms are inscribed with logarithmic and trigonometric lines, and lines used for drawing and calculating surfaces and volumes. These lines are radial from the centre of the hinge.