Nikon D300 User Manual page 437

My Recommendation: You can repeat the operation for the
other slot on the D300S if needed. Both the Setup Menu >
Format memory card and the camera button format methods
are easy to use.
Most of us learn to use the camera button method since it's so
fast. However, I'll sometimes use the Setup Menu > Format
memory card method immediately after viewing images on
the Monitor for verification of previous transfer to computer.
If it's safe to format the card, I'll just quickly switch to the
Setup Menu to format since I'm already looking at the
Monitor.
It's a good idea to learn how to use both methods.
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