The astronomically observed orbit of a mass m around a mass M is a precessing ellipse with M at one focus of the ellipse. In the Hooke Newton Leibniz theory the ellipse does not precess. This note demonstrates the equivalence of the Cartesian and offset plane polar coordinates, Eqs. (2) and (3). In the next note Cartesian coordinates will be used to produce a precessing orbit from ECE2 relativity, setting up equations to be solved numerically.