Some variable are impossible to know,control.

You are referring to an inherent characteristic of mean values, which is affecting the interpretation of *any* mean ever calculated.

As long as I don't label that value something like "The Only Truth About This Glider" it is still fair enough that's just another meaningful fuzzy datum among TONS of other fuzzy ones: reviews, opinions, rumors and, it shows, even stall speed! :-)

Thanks for your feedback Gilles and enjoy your LS6!