This proposed revision makes two key changes to Standard 133-2001. First, it decreases the difference between the dry-bulb and wet-bulb temperatures from 25 to 20°F (14 to 11° C), thus increasing the times when testing could be accomplished using unconditioned air while still not reducing the accuracy of the test. Second, it provides better flexibility by no longer limiting temperature measurement to specific types of instruments as long as they meet the requirements of ASHRAE Standard 41.1. All references were updated and ASHRAE Standard 41.2 (instead of 51) is referenced for measurement of airflow.