The taijitu is a simple geometric figure, consisting of variations of nested circles. The classical Taoist symbol can be drawn with the help of a compass and straightedge: one draws on the diameter of a circle two non-overlapping circles each of which has a diameter equal to the radius of the outer circle. One keeps the line that forms an "S," and one erases or obscures the other line. Thus, one obtains a form which Taoist texts liken to a pair of fishes nestling head to tail against each other. This basic pattern is not a pure product of human imagination, but also occurs − of less geometrical precision − in nature. In the most common Daoist variant, the two differently colored halves additionally contain one dot each of opposite color.