The rosettes on mine have never been any large than half to 1 inch
(12-25mm), and I am a little surprised that you describe a 'very long
(tall) flower stem' - my flower stems have never been more than
2-3 inches (50-75mm).
As you see above, I always think in inches and Fahrenheit when thinking
how big or how warm something is, but I go metric when writing things down.
I think youngsters in Britain these days are taught entirely metric units -
a pity in some ways - you learn a lot about arithmetic when there
are (used to be) 12 pennies in a shilling, and 20 shillings in a pound, or
16 ounces in a pound (weight) and 14 pounds in a stone - wonderful stuff!
Clarke