  We present a new technique for calibrating the primary beam of a wide-field,
drift-scanning antenna element. Drift-scan observing is not compatible with
standard beam calibration routines, and the situation is further complicated by
difficult-to-parametrize beam shapes and, at low frequencies, the sparsity of
accurate source spectra to use as calibrators. We overcome these challenges by
building up an interrelated network of source "crossing points" -- locations
where the primary beam is sampled by multiple sources. Using the single
assumption that a beam has 180 degree rotational symmetry, we can achieve
significant beam coverage with only a few tens of sources. The resulting
network of crossing points allows us to solve for both a beam model and source
flux densities referenced to a single calibrator source, circumventing the need
for a large sample of well-characterized calibrators. We illustrate the method
with actual and simulated observations from the Precision Array for Probing the
Epoch of Reionization (PAPER).
