There is variability in flow hood measurements, depending on how it\'s used, which flow hood is used, when it\'s used, etc. This variability is acceptable, as the focus of this requirement is to find problems that take the air flow well outside the range of acceptability (e.g. due to crushed ducts, large leaks, etc.). It is a matter of professional judgment, but if a rater does a couple of tests and one of them is within the +/-15% threshold, that\'s acceptable. Applicable Internationally.