Mosaic layout of the MSSS Verification Field (MVF). Left: the nine LBA fields making up the MVF, overlaid on the 10° × 10° mosaic field (central white square). The gray border around the mosaic area is a guard area used to ensure that sufficient edge fields are included and to ensure flat sensitivity within the mosaic. Right: the 32 HBA fields making up the MVF, overlaid on the same central mosaic field. The guard border is smaller in proportion to the HBA field diameter.