Ivory sector by Isaac Carver

Six-inch sector made by Isaac Carver, London, 1668-1713, and signed "Carver Fecit".

The sector has two types of scale, namely edge scales and others parallel to the edges, and sectoral scales, the latter radiating from a single point, the centre of the hinge. This sector also has some scales between the sectoral and edge ones that are unlabelled. On the front the edge scale is a twelve inch by tenths ruler. The sectoral scales are chords (labelled “C”), natural secants (labelled “Sec”), a linear scale (labelled “L”) and a segment scale (labelled “Seg”). On the reverse the edge scale is a Gunter logarithmic scale. The sectoral scales are polygons (labelled”POLL”), two tangent scales (labelled “T” and “tan”) and a sin scales (labelled “S”).

The sector was a versatile calculating instrument that could be used for a wide range of arithmetical, trigonometrical and geometrical calculations. Most calculations were performed with the sector partially opened and the aid of a pair of dividers. This is a relatively early example of an English sector and the s scale and layout differ to some extent from the layout that had become standard by the mid-eighteenth century.