Daily samplings of the four different fields F1, F2, F3, and F4 are colored in blue, red, yellow and green, respectively. Periods marked in gray show the 61 days (from April 1 to May 31) during which M31 can hardly be observed. See also Table 1. The two seasons with the highest sampling are 2000/2001 and 2001/2002, i.e., those seasons where we could combine Wendelstein with Calar Alto data.