Architectonic Sector to the Design of Thomas Carwitham, by Thomas Heath, London, 1720-30

Brass sector to a radius of 4½". The instrument follows the design of the painter and draughtsman Thomas Carwitham in his The Description and Use of an Architectonick Sector (1723): there are 3 legs, which enable two different sets of dimensions to be taken off at the same time.

On the signed side, the main sectoral scales are "F.P.C." to 32, which divides a column in plan view into its 24 flutes and fillets, "F.C." to 48 for a columns's flutes and fillets in elevation and a scale "Pol:" for polygons (12-6). The additional sectoral scale on the third leg is "Cho:" for chords (0-60). This side also has a single scale of logarithmic numbers (N) to a double radius (1-1-10).

On the reverse, the main sectoral scales are "F.P." to 29 for the flutes and fillets of pillasters, "Min" to 30 for the minutes subdividing a column's radius and "min" to 60 for the whole diameter of a column. The additional sector scale on the third leg is marked "F.I." for feet and inches and is equally divided to 12 with each unit subdivided to 12, allowing for scaling. This side also has a single scale of 4½", divided to ½, ¼ and twelfths.