Series Rec mode is specified in the factory default.
([Main Menu] [System] [Record Set] [Slot Mode] is set to “Series”.)
If both the slots are loaded with recordable cards, pressing the [REC] button starts recording only to the media in the selected slot. When the remaining space in the selected media runs out, recording continues by automatically activating the media in the other slot.
There is no indication on the display screen when the Series Rec mode is set.