From the 4500 Manual that can be downloaded as a PDF... see the link below the video on the Kestrel 4500 page

The Kestrel 4500 comes with a compass that enables wind direction readings. Usually, when the meter arrives new, it will need a calibration... These directions seem long, but in reality, it takes about 3 minutes to do, sometimes less, and it's really simple. You will have to calibrate every now and then, as with any digital compass.

Calibrating the Digital Compass:

Due to the magnetic signature of the AAA batteries, the Kestrel 4500’s digital compass must be calibrated, or “taught” to correct for the magnetic field of the batteries. This must be done each time the batteries are changed or the battery door is opened. If your unit has not been calibrated, it will display “uncalibrated” at the base of the Direction, Crosswind and Headwind screens and will not display or log any values until it has been calibrated. When calibrating the compass, be sure to choose a location that is not near metal or magnetic materials. For example, you cannot calibrate the Kestrel Meter reliably on a metal desk. Also, keeping the Kestrel Meter vertical (front/back and left/right) is crucial to accurate calibration. The foam stand included in the Kestrel Meter’s packaging will help to stabilize the unit during calibration. (The piece is also handy for standing the Kestrel Meter up while taking readings in the field.)

Finally, removing the impeller during calibration is recommended. (Simply press on the edges of the impeller to pop it out, then press it back in after calibration is complete. Align the small triangle on the impeller housing with the matching triangle near the hinge of the impeller cover on the front of the unit.) To calibrate the unit’s digital compass, press the button to enter into the Main Menu, and use the button followed by the button to select System. In the System menu, select "Compass Cal."

Following the screen prompts, place the Kestrel Meter in the foam stand and slowly spin it around three full times. Each rotation should take approximately 10 seconds. “Cal Complete” will be displayed on the screen when the calibration is finished. Press the button to exit out of the Menus.

After calibrating, you may wish to verify the digital compass’ accuracy with a compass that you know to be operating properly. Being careful to orient the Kestrel Meter vertically, verify the readings at north, south, east and west. (It is possible that some but not all of the directions would be correct if the unit is not calibrated correctly.) Remember to hold the Kestrel Meter and the compass far enough away from each other that they do not interfere. You should expect the Kestrel Meter’s readings to be within ±5° of the reference compass or better. If the Kestrel Meter’s direction readings do not appear to be correct, simply run the calibration routine again.

Once your unit is correctly calibrated, you do not need to calibrate again unless

a) you change the batteries or open the battery door;

b) the unit displays “uncalibrated” at the base of the Direction, Crosswind or Headwind screen.

Calibration Error Messages

There are three error messages you may see during calibration. They are:

Magnetic Batteries: In some instances, the magnetic field of the batteries is such that the Kestrel Meter cannot accurately calibrate the compass. If this is the case, upon completion of the three rotations the screen will display this error message. Simply open the battery door, rotate one or both of the batteries slightly, and run the calibration again.

Too Slow: The unit was spun too slowly during the calibration routine. Press the button to remove the error screen, and then follow the directions on the screen to calibrate.

Too Fast: The unit was spun too quickly during the calibration routine. Press the button to remove the error screen, and then follow the directions on the screen to calibrate.