The question amounts to how many unique combinations of 4 objects out of 12 are there? This is given by the formula: 12*11*10*9/(1*2*3*4)=495 or 12C4. The objects are the points on the circle, which can be represented by the numbers on a clock face. Pick any 4 numbers out of 12. Let's choose 7, 4, 12, 1. Put these in order: 1, 4, 7, 12 and join up these points and join 12 to 1 forming the 4-sided figure 1-4-7-12-1. All possible 4-sided figures can be represented by a unique combination of numbers by placing them in numerical order, assuming that the figure is a quadrilateral and not, for example, a figure that looks like two triangles perched on top of one another on a vertex, like an X with joins at the top and bottom. So 495 combinations represents all possible quadrilaterals. A square, for example, would be 1-4-7-10-1 (same as 7-10-1-4-7), 12-3-6-9-12 (same figure as 3-6-9-12-3), etc.