HP 54710A User's Reference Manual page 94

Calibration Overview
Best Accuracy Calibration Level
For the best measurement results, a channel (plug-in/slot combination)
should be calibrated to best accuracy level. Also, two wide plug-ins must be
calibrated to best accuracy level to give accurate results in real-time mode.
The best accuracy calibration level has a temperature ∆ associated with it,
just like the mainframe calibration. This temperature ∆ appears in the
"Plug-in" calibration status screen for all plug-ins under the
"Utility/Calibrate/Cal status on" menu and for each plug-in under the
"Channel/Calibrate/Cal status on" menu.
In order for a channel to meet the specifications listed under "Best Accuracy"
in chapter 16, both the "Current frame Temp ∆" and the "Best Accuracy
Temp ∆" must be between ±5 °C. In other words, the oscilloscope must be
within ±5 °C from the temperature that the mainframe was calibrated at and
within ±5 °C from the temperature that the best accuracy calibration was
calibrated at for a particular plug-in slot calibration.
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