Polar Planimeter: a Mechanical Analog Computer By J. Halden.

The Planimeter is the first instrument used for measuring area by continuous integration. The German engineer, J. M. Hermann, invented it in 1814. The first complete Planimeter was invented by Johannes Oppikofer and exhibited by him in Paris in 1836. A patent on a Planimeter was granted in 1849 to Kasper Wettli and George Starke. The Swiss scientist Jacob Amsler invented the modern polar Planimeter in 1854. This Halden Planimeter is a marvel of mechanical skill and mathematical calculating accuracy. Made from German silver and steel with an option to alter the radius of the tracing arm. The results are read directly with the aid of a vernier. J. Halden & Co. was established in 1877 in Rowsley Works, Reddish, Manchester. The manufacturing company was famous for its ‘Halden Calculex Circular Slide Rule’ and various measuring, drawing and surveying instruments. The company became J. Halden and Co. Ltd. as late as 1930 with an office in London.