The Equationor or The Universal Calculator

Wanted: The Equationor

The Equationor, or the Universal Calculator, was invented, patented and copyrighted by Walter Hart of New York. The device, a combination slide rule and calculator, was produced by the Equationor Company, also of New York. Its patents date it to March and July of 1888, September of 1889 and April of 1890.

Have one for sale? Please email me at or call +1 860 729 2252