Thanks RAT5 and others. I personally always use a buffer to allow for changes. Like I said, this was just from a legal perspective. Can we depart with less headwind than calculated, legally? Most guys I see use the exact figures on the atis to calculate, based on perhaps 30 mins old values. You could have temperature changes of 4-5 degrees and much different wind components. I think it is wise for any company to have guidelines for, when we need to do a re-calc. Makes it easier for everyone with a set of rules, except just the opinion of the individual in the left seat.