The Diff is a unique instrument developed by Observator to measure the air flow rates. The DIFF is self-adjusting for inlet and exhausts grilles, it can automatically detect the flow direction so the DIFF does not need to be turned around when changing the grill. For your convenience you are able to set the arms and the display unit in any position. This will make it easy to operate and to read the display therefore eliminating the use of a ladder in most cases.