With a replacement impeller on hand, you can be sure your Kestrel is always ready to provide fully accurate wind or air flow measurements. Each impeller is individually calibrated in our NIST traceable wind tunnel to Kestrel specifications and comes with its own Certificate of Conformity. Simply replacing the impeller in any Kestrel meter of any age restores factory calibration. And the best thing Replacing your impeller is hassle-free and tool-free  just press the new impeller into place, popping out the old one at the same time. Thats a Kestrel patented feature. Field impeller replacement is a breeze, so maintaining Kestrel accuracy is too.