I'm going to check the tire pressure. That's the only thing I can think of why it was 1/2 inch off. I know that a pound of air or so can really make a difference.
To adjust there's just two bolts to mess with on each side. One you loosen and one you turn clockwise to raise and counter clockwise to lower. If its the tire pressure I bet that I raised it and didn't even need to adjust the deck 1/2 up. If its not the tire pressure.