When the mean anomaly M is computed, the goal is to compute the true anomaly θ. The function θ = f (M) is, however, not elementary. Kepler's solution is to use E = ∠ ∠ z c x , x as seen from the centre, the eccentric anomaly as an intermediate variable, and first compute E as a function of M by solving Kepler's equation below, and then compute the true anomaly θ from the eccentric anomaly E. Here are the details. | z c y | = | z s x | = | z c x | − − | s c x | w i t h | s c x | = | c s | . | d x | 2 a 2 M 2 = a 2 E 2 − − a ε ε ⋅ ⋅ a sin ⁡ ⁡ E 2