This option is thought to be mainly useful for observations of solar-system objects and specifies that the 12- and 7-m arrays should observe simultaneously (at the same time, for the same amount of time). If this is requested, it must be the case that only a single 12-m configuration and the 7-m array are required or a validation error will result. As implied, the 7-m time will be set to the same as the 12-m. Unlike other observing modes, it is possible to use any 12-m configuration together with the ACA. Please note that configurations C-7, C-8, C-9, and C-10 are however excluded from simultaneous observing, as they cannot be paired with ACA.