  We give formulas for a canonical choice of grading and compatible affine
connection on a sub-Riemannian manifold. This grading and affine connection is
available on any sub-Riemannian manifold with constant symbol and is based on
Morimoto's normalization condition for a Cartan connection in such a setting.
We completely compute these structures for contact manifolds of constant
symbol, including the cases where the connections of Tanaka-Webster-Tanno are
not defined. We also give an original intrinsic grading on sub-Riemannian
(2,3,5)-manifolds. We use this grading to give a flatness theorem for such
manifolds and explain how the grading and connection from Morimoto's theory
compare.
