Nikon D300 User Manual page 686

Storing White Balance Values for
Future Use
If you have previously used the manual "measured" PRE
method to set the WB, you will already have a value in WB
memory location d-0. You can keep up to five WB values
stored in your D300(S). In location d-0 you'll find the current
PRE WB, and in d-1 through d-4 you'll find any stored WB
values. They appear as tiny images, as shown in Figure 10-5.
If you shoot under a certain light source on a frequent basis,
such as in a studio, you may want to store one or more of
your PRE White balance values in one of the four permanent
storage areas in your camera (d-1 to d-4).
I tried to enter a White balance measurement directly into one
of the d-1–d-4 memory locations by selecting the location
before doing the light measurement. However, my values did
not show up in d-1–d-4 but instead overwrote the value in d-0
each time. It is only possible to copy a value from d-0 into
one of the four storage locations. I suppose Nikon was
concerned that one might accidentally overwrite a carefully
prepared White balance setting, so it added a copy step
between the measurement and long-term storage.
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