  This study aims to improve the photometric calibration of astronomical photo
plates. The Sonneberg Observatory's sky patrol was selected, comprising about
300,000 plates, and the digitization workflow is implemented using PyPlate. The
challenge is to remove zero point offsets resulting from differences in color
sensitivity in the photo plates' emulsion response. By utilizing the Gaia DR3
dataset and the GaiaXPy tool, we are able to obtain a consistent astrometric
and photometric calibration of the Sonneberg plates and those of other archives
such as APPLAUSE.
