Comparison of photometric precision in two fields of NGC 330 captured during the nights of 17 and 19 December 2008. Three upper panels: photometric errors from DAOPHOT for V, (b − y) and m1 (black points for the field from the first night, gray from the second). Three bottom panels: differences in metallicities determined for the first and second field for clusters, and old and young field giants, respectively.