The Little Professor is a backwards-functioning calculator designed for children ages 5 to 9. Instead of providing the answer to a mathematical expression entered by the user, it generates unsolved expressions and prompts the user for the answer.

The calculator was a relatively affordable learning aid, marketed at $20. It’s thought to have sold more than one million units in 1977 alone.

Taking the shape of a mustachioed, bespectacled man reading a book, the calculator came with a book entitled Fun with Math Facts. The short book promised ’18 Learning Games and Activities with the Little Professor’.

Developed by Texas Instruments, who had invented the handheld calculator in 1967, the Little Professor was released on June 13th, 1976, and is widely credited as the world’s first electronic educational toy.

A second-generation version of the Little Professor was released a few years later, with a solar-powered version following in the early 2000s.

The calculator is similar to Dataman, another electronic educational toy released by Texas Instruments in 1977. This version resembles a robot and, as per its sci-fi theming, was aimed at older children.

While long-discontinued, an emulator of the Little Professor was created for Android mobile systems in 2012.