The American William Hart patented this appealing little adder/calculator in 1878 and called it ‘Hart’s Mercantile Computing Machine’. Constructed with 3 concentric brass rings and a central steel needle, it could assist with calculations up to 9,999.
According to the information provided by the Smithsonian, by 1888 Hart had only sold 3,500 of these devices but had ordered 1,000 more. It is therefore fair to assume that less than 4,500 of these little adders were ever sold making it a rare little device today with only a few current known survivors. Further information about this adder can be viewed by clicking here.
It measures 13cm diameter and is on a later hardwood base. The brass has been lightly polished only to retain its character, and everything rotates smoothly as it should.
