  The Qweak experiment aims to measure the weak charge of the proton to 4% via
the parity-violating asymmetry ($\sim$-200 ppb) in elastic e+p scattering. The
scattering rate is largely influenced by five beam parameters: horizontal
position (X), angle (X'), vertical position (Y), angle (Y'), and beam energy
(E). Changes in these parameters when the beam polarization is reversed will
create a false asymmetry. To measure the detector sensitivities, we modulate X,
X', Y, Y' using four air-core dipoles in the Hall C beamline as well as beam
energy with a superconducting RF cavity. Linear regression is then used to
remove the false asymmetry. The beam modulation system has also proven valuable
for tracking changes in the Hall-C beamline optics including dispersion at the
target.
