That's a big swing in temperature. Depending on what the starting conditions were, a 9 deg C. increase in temp can mean 2-3% decrease in air density, and also a decrease in Crr. The smaller the change in position or equipment, the more careful you have to be in tracking changes in conditions. Was the difference between the 40 and the 44 on that order of size, or was it larger than that?

[edited to add:] This method is sensitive enough to detect changes in the weight of air. Fortunately, if you keep track of the temperature and barometric pressure (humidity makes a small amount of difference, too) you can calculate the weight of the air and account for it. That's pretty cool.