The six twenty-two meter diameter dishes of the Australia Telescope Compact Array spend almost all their time with all dishes looking in the same direction. The signals for the dishes are then combined in real time to synthesise a telescope up to 6 km in diameter. As the picture above illustrates, however, on occasions it appears one dish "didn't get the memo" about when and where to point! This is most often the case during scheduled maintenance periods, when one antenna is stowed for engineers to access the antenna drives, cryongenic cooling systems, and electronics equipment for regular check-ups. While this is happening the remaining dishes can be used to conduct other on-sky tests of the array's performance.
