ok to attempt to pull this back to the original question without a PhD involved.... Why get type 1 and 4 when it's just frost or maybe a very light snow? Because many hub stations are now diluting the type 1 so thin that it's mandatory to put type 4 on even if there is no active precipitation. It's called a blended station and gives no option to just use type 1 because the type 1 is so diluted it doesn't meet the minimum freeze spread... the bean counters say this method is cheaper... I don't give two hoots as I keep breaking guarantee on reserve and this just adds to it. Most block times are now accounting for this in winter, and the few that don't mean the bean counters had best planned for the fuel burn to try to make up that extra time deicing.

Drops mike and grabs a glass of Bourbon and a cigar