The Hercules cluster was observed with the 2MASS 3-channel camera on the night of 970521. Five repeated scans (047 to 051; each six degrees in length) were acquired with the Hercules cluster located roughly in the center of the scan. The conditions were photometric, with an internal photometric zero mag offset of less than 2% between the 5 scans. (The maximum offset was 2% at J, between scan 051 and 047).
An additional six scans of the same field were acquired immediately following the five noted above, but the exposure time was decreased to 1 second per frame. The motivation for this change was to test the utility of shorter exposure times. Unfortunately, it means that this data is not usable for the repeatibility analysis task at hand (it would require scaling the images, noise measurements and other repeat measurements, thus imparting an uncertainty that is highly undesirable). Therefore these six scans are discarded from further consideration.