A qualified technician uses an anemometer to set air flow and calibrate the alarm. There are 4 screws holding the face plate on the alarm that have to be removed. Under the faceplate, there is a circuit board which has a set button and a delay button. The set button is for the low air flow point. (If air flow drops below this point, the alarm will sound indicating it may be time to change the filter.) Once the set point is established, the delay point should be turned out to the full 30 seconds. This allows the user time to open the door to put equipment in or take it out without having to hear the alarm. Once the set point and delay point are set, replace the cover on the alarm. Then the air flow should be increased for the operation point. Optimal performance is 75 linear feet per minute, plus or minus 5, for operation.