Summary: When trying to build a large set of ground based SpectroPhotometric Standard Stars (SPSS) for calibrating Gaia BP/RP Spectra and G-Band Images to a few % in absolute flux, it is essential to maintain the maximum homogeneity in data quality, acquisition and treatment. This is especially true when data come from different observing sites around the globe and are obtained and treated by different persons. The Observation Protocols and the Data Reduction Protocols are sets of detailed instructions for observers and collaborators that participate in the large effort required. This second Observation Protocol concerns photometric observations obtained during: (i) auxiliary campaigns aimed at excluding variable stars from the main list of candidate Primary and Secondary SPSS and (ii) photometric campaigns for the absolute flux calibration of SPSS spectra taken in non-photometric nights.
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