i totally suck at math, however i think i know what is a circle, i can draw one with a compas. then i think i know what is the diameter of this circle, i can draw it by drawing two more circles and a line with a ruler. because a mathematician told me that the product of this diameter by a number is the circumference of the first circle i believe him, but if another mathematician ask me to draw two more circles and another line to define the same circumference... i will probably believe that the first one suck less than the second one at maths! (sorry for my english!).