The Calibration Kit allows you to perform dozens of recalibrations in the field, to ensure that your Kestrel is always performing within specifications.  In fact, if using distilled water, you can calibrate an indefinite number of times.  

The manual explains in detail all of the steps for recalibrating your Kestrel. This process will take approximately 13 hours (about 15 minutes of work), including setup and calibration. The RH (calibrate humidity sensor) calibration kit includes the following items:

• three clear, sealable containers
• one container with magnesium chloride solution
• one container with sodium chloride solution
• two wooden scrapers
• an insulated carrying case to hold all of the above and maintain a stable environment while performing calibration
• For use with: Kestrel 4500, Kestrel 4300, Kestrel 4200, Kestrel 4100, Kestrel 4000, Kestrel 3500, and Kestrel 3000 (Both the older 2 button and 4 button version)

How often do meters need to be re-calibrated?

Largely it’s dependent on whether it’s industrial use or consumer use. Acousticians recalibrate annually, firefighters annually or semi-annually, and general consumers might recalibrate them every 4 or 5 years or so. The official stance is that a calibration is recommended every 24 months due to the possibility of up to 2% calibration drift over 24 months.

Kestrel Calibration Kit Additional Information 

• Kestrel Calibration Kit Instructions (PDF)
• Weight 1.5 lbs / 680 grams
• Place of Origin: USA