This is why I have an official board, for the official measurements...and I have a personal one, that I clear half of every hour or so, and leave the other side alone for the entire event... strictly for my personal data analysis, but the board is what I report... I have been back and forth with people who argue with me about how much actually feel, because they are measuring from a driveway or heated car hood, but fail to grasp the nws board cleaning process.. btw, the difference in all the measurements are sometimes substantial, sometime not, ratio dependant