We kicked the tyres on this one in the staff coffee room. Issues of Mathematics, Systems Engineering and Language were raised. Mathematically, a circle is a set of points, an abstract concept. It is possible to draw a diagram approximately (but not accurately) illustrating a circle but - for a start - the drawn circumference will have non-zero width and so is rather an illustration of an annulus than a circle. I have felt it necessary to indicate the difference between a 'model' and a diagram of that model in classes on Enterprise Architecture. The notation (if defined) can be changed in minor ways without changing the meaning. In Systems Engineering terms, as FL pointed out, one need other things to draw the circle physically rather than conceptually ... paper, table, (drawing agent) and pencil if it was not included with the compasses. Most people would forget the drawing agent ... but people are often a component of 'soft' systems. But then, if one hold up a picture of a circle to a class of children, they will say they see a circle. Formal language without overloaded words would make informal communication more difficult. Guy