A simple version of the Eratosthenes mesolabium that finds square roots. (This will find square roots of numbers between 0 and 1.)

Move point *C* up and down using the mouse until the length of *CH* is the desired value. Then use the mouse to move triangle *QSH* back and forth until point *B* is on the line from *A* to *C*. Then the length of *BG* will be the square root of the length of *BH*.

(This is based loosely on pp.184-185 of David Burton, *The History of Mathematics: An Introduction, Seventh Edition*, 2011, McGraw-Hill.)