(See http://www.geogebratube.org/material/show/id/8222 for anothernew version.)[br][br]Drag the green point to appropriate position to measure the diameter of the circle.[br]Drag the red point P to straighten the circumference. Divide the scale of the ruler to measure its length to [b]two decimal places[/b]. Use the Zoom In, Zoom Out and Move tools if necessary.[br][br]Calculate the values of c/d. What do you discover?

Anthony OR. GeoGebra Institute of Hong Kong.