  An atom interferometer using a Bose-Einstein condensate of $^{87}$Rb atoms is
utilized for the measurement of magnetic field gradients. Composite optical
pulses are used to construct a spatially symmetric Mach-Zehnder geometry. Using
a biased interferometer we demonstrate the ability to measure small residual
forces in our system at the position of the atoms. These are a residual
magnetic field gradient of 15$\pm$2 mG/cm and and an inertial acceleration of
0.08$\pm$0.02 m/s$^2$. Our method has important applications in the calibration
of precision measurement devices and the reduction of systematic errors.
