I searched around for updated documentation when I got the alert about rc3 - all I could find was the change log file that I linked to. I presume a fully updated doco file will come later - perhaps when it's no longer just a release candidate.
I think the main change is the frquency calibration mode that has been added:
Improved frequency calibration
Measure check box added to FreqCal mode, check to record to fmt.all
with current calibration correction disabled, uncheck to see the
impact of the current calibration parameters.
The fmt.all file is now optionally renamed to fmt.bak when a
calibration solution is accepted. This allows users to preserve an
fmt.all file that they might have edited for best fit.
A calibration procedure might proceed thus:-
1) select FreqCal mode,
2) step through suggested calibration test frequencies deleting those
that have no usable signal,
3) enable "Menu->Tools->Execute frequency calibration cycle" and check
that suitable signals are present,
4) select a suitable FTol and T/R period,
5) check "Measure" and let the cycle complete a few times to gather
6) uncheck "Measure" to complete the data capture, optionally tidy the
fmt.all file with your favourite editor,
7) push "Menu->Tools->Solve for calibration parameters" and accept if
you like what you see,
8) sit back and admire your accurately frequency calibrated station.