HP 54710A User's Reference Manual page 108

Channel Menu
Calibrate
Current Frame ∆Temp This is the temperature change inside the
instrument from when the last mainframe calibration was performed. A
positive number indicates how many degrees warmer the mainframe is
compared to the temperature of the mainframe at the last mainframe
calibration.
Channel Calibration Level The oscilloscope displays Best, Normal, or
Uncalibrated, depending on the present calibration level of the plug-in.
Best means that a best accuracy calibration was performed on the plug-in.
For the best accuracy calibration to remain valid, the current temperature ∆
and plug-in best accuracy temperature ∆ must be within ±5 degrees, and no
more than 24 hours has elapsed since the best accuracy calibration was
performed.
Normal means that the plug-in is not calibrated for best accuracy. Either the
calibration factors were cleared from the memory in the mainframe, or that a
best accuracy calibration was not performed on this plug-in in this slot. Also,
Normal indicates that the normal plug-in calibration is still valid for this
plug-in, and all you have to do to gain back the one percent accuracy
specifications is perform a best accuracy calibration.
Uncalibrated means that the normal plug-in calibration is invalid. You must
calibrate the plug-in to normal accuracy before performing a best accuracy
calibration. To calibrate the plug-in, see the Service Guide that is supplied
with the plug-in.
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