SOLD This unusual, early sector is square in cross-section, and each limb houses a pair of dividers. The design, construction and numbering style are all typical of the period around 1700. The sector has the following scales:
Recto: Line of lines, marked ‘L’ on each arm, numbered 1-10, and each unit divided to 20ths, and a rule of English inches, divided to 8ths.
Verso: Line of chords 0-60 marked ‘Cho’ on each arm, divided to a half degree; Gunter’s line 1-10-10.
The outside of the instrument gives a line of equal parts, with 100 divisions. There is no signature.
Each arm holds a pair of dividers, which screw into position. The larger pair is certainly original, and screws perfectly into position.
The smaller pair, although appearing very similar, is constructed without a steel leaf in the hinge, does not screw fully into the arm, and is (in my opinion) a later (but still very old) replacement. The sector may have originally housed a crayon-holder or pen, rather than a second pair of dividers (see below).
I cannot find another example of a sector like this, but in the Oxford Museum of the History of Science (inv. no. 30151), there is a silver rule by John Rowley, of square cross section with Gunter’s line, line of equal parts, and other scales. It houses a pair of dividers in one end, and a crayon-holder in the other. It is illustrated in Hambly's Drawing Instruments 1580-1980 p.130.