The unit of NoRH observation is called schedule. In principle, one day has one schedule. But when some trouble happens to the observing system, there may be multiple schedules. The schedule ID is given to identify each schedule. They are "date + an alphabet letter". That may be only "date" if there is only one single schedule per day. For example, the schedule ID on July 10, 1992 is "920710" because there was only one schedule on that day. On the other hand, there were two schedules "920712a" and "920712b" on July 12.