A 1921 comptometer is worth around $149 in good condition. The comptometer was the very first successful key-driven mechanical calculator that was patented by Dorr E. Felt in the year 1887.

The high end toy company Ertl was established in 1945. Company founder Fred Ertl expanded his production in 1959 and ultimately, the company was acquired by Victor Comptometer Corporation in 1967.

Produced in the 1940s. This was the first Fell and Tarrant machine to have keys the same height above a sloped face plate and it was driven by an electric motor.

A model H was recently offered for $35 and a K must be double that at least.

James Robert Meehan has written:

'How to use ten-key adding machines' -- subject(s): Calculators

'How to use the calculator and the comptometer' -- subject(s): Calculators, Comptometers

'Clerical office procedures' -- subject(s): Office practice

'Secretarial office procedures' -- subject(s): Office practice

Calculators have changed drastically the first calculator was an abacus. The Arithmometer (1820) was for add, subtract, multiply, and divide. The Odhner (1875) was made by Odhner who invented a pinwheel calculator which used a hand crank to complete the computation. The Comptometer (1885) was made by Felt, he invented the first calculator using keys to push for number entry and calculations. The Standard calculator (1901) was made by Hopkins who used two rows of five buttons representing the digits 0 through 9 to perform math computations. The standard ten digit keyboard (1911) we use today was made by Sundstrand who brought the design from Sweden to the United States. The first commercial calculators (1914) began entering businesses and the use of calculators began to be popular. We have been modifying calculators a little at a time since then.