Flow benches can give different reading due to weather changes (barometric pressure, temperature, etc.) but if you know what your doing there's a calculation you do using all those #'s that gives you a corrected reading. You have to know how to do these calculations correctly because weather conditions can change in just a few hrs., or even less sometimes, and if you don't calculate the correction factor right you won't even be able to trust your own figures done on different days.
