Tex, you need to delete the old runs for the box to be able to predict accuratley when the weather is changing from race to race is what i was told by Performaire when I talked to them earlier this year. I now delete all previous runs from the race before unless the weather conditions are real close(2 to 5 degrees F and 10% humidity and within .30 Barometric pressure) to being the same as the last race I was seeing inaccurate predictions with the old weather in the box, it became a lot more accurate when I started deleting the old runs B.P and humidity really play havoc on most N/A motors on gasoline, no matter how good the tune up is