  For any Legendrian knot in (R^3,ker(dz-ydx)), we show that the existence of
an augmentation to any field of the Chekanov-Eliashberg differential graded
algebra over Z[t,t^{-1}] is equivalent to the existence of a ruling of the
front diagram, generalizing results of Fuchs, Ishkhanov, and Sabloff. We also
show that any even graded augmentation must send t to -1.
