No is doesn't change quite like that.The differents are not that far Off. Not that i ever seen a few CFM at most. Nothing like 10,15,20 point difference. But then again I have never taken a head from the south to the North or the East,west.Nore have i seen weather make that type of change either.

Larry/Twisted6
[oooooo] smile
Adding CFM adds boost smile
shocked God doesn't like ugly.