Nikon D6 Reference Manual page 791

Copying Pictures
1
Choose [Select source].
Highlight [Select source] and press
2 to display [Select source] options.
2
Select the card containing the
pictures to be copied.
Highlight the slot for the card
containing the pictures to be copied
and press J to select the highlighted
slot and return to the [Copy
image(s)] menu.
D The Playback Menu: Managing Images 739