The rate at which the LRL vector rotates provides information about the perturbing potential h (r). Using canonical perturbation theory and action-angle coordinates, it is straightforward to show that A rotates at a rate of, ∂ ∂ ∂ ∂ L ⟨ ⟨ h ( r ) ⟩ ⟩ = ∂ ∂ ∂ ∂ L { 1 T ∫ ∫ 0 T h ( r ) d t } = ∂ ∂ ∂ ∂ L { m L 2 ∫ ∫ 0 2 π π r 2 h ( r ) d θ θ } , where T is the orbital period, and the identity L dt = m r dθ was used to convert the time integral into an angular integral (Figure 5). The expression in angular brackets, ⟨ h (r)⟩, represents the perturbing potential, but averaged over one full period; that is, averaged over one full passage of the body around its orbit. Mathematically, this time average corresponds to the following quantity in curly braces. This averaging helps to suppress fluctuations in the rate of rotation.