This 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 a couple of days, including setup and calibration. For use with all 5000 series Kestrel meters, and all discontinued 4000 Series Kestrel meters. The Kestrel 3500, and Kestrel 3000.