Sundstrand 10 Key Adding Machine - 1920
"A ten key portable machine. The first models put on the market in 1914 and in September, 1923, the direct subtracting model was announced. All models have the keyboard arranged in three rows of three keys each, with a bar or cipher key below; control keys are arranged along either side of the amount keys. A back space key allows the user to remove entry errors.

This elegant design pictured here was most likely produced in 1920, and was sold for approximately $300. View a 1941 ad for a similarly designed model."

Source: Dr. Tim Bergin, Eric Ashman, Seth Gordon, Jeana Scheirer, Dave Muehling and Andrew Hewitt, "Mechanical Computing."

X-Number World of Calculators