Hezzanith Mark 1 Fields Rule.
The parallel rule was invented by Fabrizio Mordento about 1584. Little used, it became more accepted in the late eighteenth century. Captain William Andrew Fields, (1796-1871) improved the design by adding a protractor-style scale to the upper edge and compass points to the opposing edge which facilitated the reading of the compass bearings.
Hezzanith was the trade mark of Heath and Co, who later became part of W. F. Stanley.
The Mark 1 rule added a third rule . The unusual links give a much wider range of movement than the usual parrallel rule and the upper and lower arms remain in line.
Ebony.
Length. 38.5 mm. (15 inches).
Good condition with obvious indications of use.