He then went into the arithmometer, which is arguably the first commercially successful mechanical calculator with four functions. That was around 1821 or so. But [Dan] mentions it used a Leibniz ...

Prices dropped as new features were added and sales doubled each year. By 1976, a four-function calculator cost only a few dollars. In 1972, 5 million calculators were sold in the US and within ...

Desmos offers a variety of math tools online. Many are calculators, including “a four-function, scientific, and graphing ...