I invoke it just prior to the print job:
but unless there’s a log somewhere that I haven’t seen, it never tells me what the flow dynamics number was.
What I do know, though, is that if I, for example, change the filament temperature, then I should set the Flow Dynamics Calibration to “On” rather than “auto”, because it doesn’t seem to realize there’s been a change, and so (I presume) it re-uses an obsolete K value. If I set it to “ON”, though, it seems (?) to recalibrate using the new temperature and the print comes out fine.