English, c. 1818-1820, an early version of this three-foot rule in boxwood and brass, double sided with numerous finely divided logarithmic scales and early form of cursor, time side with scales marked for Tangents, Latitude Sines, Diff TD, Time PM, Time AM, Azimuth; lunar side with scales F Distance, S Distance, Hor Par, Alt, and a full length logarithmic number scale, signed 'Bate London no 110', one edge a 36 inch rule divided in tenths, length 95cm overall.

Note: For determining longtitude at sea. This rule was designed in 1816 by David Thomson (1789-1834), an Arbroath merchant captain. The lunar distance method continued to be used well into the 19th century until marine chronometers became more affordable.