  We develop a general method to "self-calibrate" observations of galaxy
clustering with respect to systematics associated with photometric calibration
errors. We first point out the danger posed by the multiplicative effect of
calibration errors, where large-angle error propagates to small scales and may
be significant even if the large-scale information is cleaned or not used in
the cosmological analysis. We then propose a method to measure the arbitrary
large-scale calibration errors and use these measurements to correct the
small-scale (high-multipole) power which is most useful for constraining the
majority of cosmological parameters. We demonstrate the effectiveness of our
approach on synthetic examples and briefly discuss how it may be applied to
real data.
