Nikon D6 Reference Manual page 171

Option
[JPEG fine c ]
[JPEG fine]
[JPEG normal c ]
[JPEG normal]
[JPEG basic c ]
[JPEG basic]
A
Dual-Format Recording
•
If you select [RAW Slot 1 - JPEG Slot 2] for [Role played by card in Slot
2] in the photo shooting menu when taking pictures with a NEF (RAW) +
JPEG option selected for image quality, the NEF (RAW) copies will be
recorded to the card in Slot 1 and the JPEG copies to the card in Slot 2.
•
If a JPEG option is selected for image quality and [JPEG Slot 1 - JPEG
Slot 2] is selected for [Role played by card in Slot 2], the camera will
record two copies of each picture, one to each memory card and each at
different sizes.
Description
Record photos in JPEG format. Image
quality increases as quality progress from
basic through normal to fine. Options
with a star (" c ") prioritize image quality,
those without a star (" c ") file size.
The T Button 119