Description and Notes:
This is the first of the only two known commercialized drawing compass designs which utilized the parallel four-bar linkage to maintain both points in vertical orientation and for self centering the handle. The other one is the "Original Lotter parallel compass" devised in the 1950s.
On one side bar of the compass stamped a patent number "PAT 439 - '10." This consistent with the UK patent numbering system from 1852 to 1915, and which means the 439th patent granted in the year of 1910. However, as according to the Museum of Science and Industry, the manufacturer, J. Halden & Co., only have branch in London by 1920, this set can probably be dated to the 1920s.
With the extension arms attached to the main body, this compass can draw circles with radius up to 9.5 inches (or about 24 centimeters). This set appears to be individually hand made as there is an identification number, 77, stamped on every component. It also comes with a finely made leather covered wooden case with a push button in front.