Global upper air temperature measurements from routine radiosondes often do not report accurate ambient air temperatures, even when the same radiosonde type is used. The Accurate Temperature Measuring (ATM) radiosonde, developed at Wallops Flight Facility, provides true temperatures with an accuracy of 0.2°C. The ATM radiosonde is used to compare temperature measurements from operational radiosondes. Although there have been improvements to many of the modern radiosondes, errors when compared with the ATM radiosonde are found to be as large as 0.8°C after corrections were applied to the measurements. In this paper we summarize results of our study.