Invented by physicist Ilan Samson, the Quick Approximate Mental Arithmetic (QAMA) Calculator will only reveal the answer to your mathematical query if you already have a good idea of the answer. You might want to get a second calculator to use this one.

After entering your equation, you’ll have to enter a reasonable estimate of the answer before QAMA gives up the exact result. Samson’s goal in inventing the calculator is to keep students thinking and not be overdependent on calculators.

Fortunately, the QAMA can be quite forgiving if needed. It has a normal mode where it will provide the answer outright, but the device will flash its lights while it’s in this mode, alerting the people around you of your laziness. Even in its default estimate mode, the QAMA will eventually provide the correct answer if you give an incorrect estimate five times, but not without a slight delay to urge the user to think.

Head to the QAMA website for more info on this unique calculator. Unfortunately for Mathletes the online store is down as of this writing. Maybe we need to provide a good estimate of the calculator’s price before we can buy one.

[via Reddit]