circle pi

Archimedes' method for calculating pi is fairly well demonstrated using this programme. It is best to open the 'pi graphics' box to a full screen and then the 'pi controlling' box within it.

Note that to close these two screens you have to click inside the given box (as it explains).

illuminations NCTM pi and visualising equation solving

Computing pi - the Archimedean 'squeezing' a circle between polygons method; compares accurate to approximate areas and circumferences

Pan balance-expressions - set up equations with an expression in each pan balance (one could be a constant or zero) and use a slider to see where the two expressions have the same value. Especially good for seeing how the solution fits two linear expressions (i.e unknown on both sides of an equation, viewed as line graphs).