Calibrating my power tap was the worst thing that ever happened to my power numbers... LOL. It's been very consistent over the years but I replaced the batteries on Monday right before my ride and holy power output! My garmin mount is busted so I ride with it in my jersey pocket and didn't see it coming.
Speaking of which, Garmin is going to swap it out for a refurbished Garmin 800 for $25, which I consider highly reasonable.