How to find the centre of a given circle.
Writing about web page http://www.mathematica.gr/forum/viewtopic.php?f=57&t=262
Trying to make my own clock, using a circular canvas, the first thing I needed to do was to find its centre. How can one do this: Pick any point of the circumference (call it P) and draw an arc from circumference to circumference. Use the two intersection points of the arc with the circumference to draw 2 new circles (or arcs), with the same radius as the first one. The 2 new circles meet at the centre of the first circle as well as at a second point, Ã. Use Ã as the centre of a new circle with radius ÃP. This new circle intersects with the very first arc drawn at 2 points, call the Ä and E. Use the 2 points as centres of circles of radii ÄÑ and ÄÅ. These 2 final (!!) circles meet at the centre of the circular canvas started with. There is an image of this construction at the website above (instructions of the website are in Greek nevertheless!)