  We present a method for determining the phase and contrast of a single shot
of an atom interferometer. The application of a phase shear across the atom
ensemble yields a spatially varying fringe pattern at each output port, which
can be imaged directly. This method is broadly relevant to atom interferometric
precision measurement, as we demonstrate in a 10 m Rb-87 atomic fountain by
implementing an atom interferometric gyrocompass with 10 millidegree precision.
