These measurements are primarily for passive detectors under “known” exposures in a radon calibration chamber. The samples are labeled and submitted to the laboratory in the same manner as ordinary samples to preclude special processing. The results of these measurements are used to monitor the accuracy of the entire measurement system including the routine performance of personnel. Both laboratory suppliers and secondary placement companies should arrange for the regular introduction of spiked samples for routine analysis as part of their QA plan. Providers of passive measurement devices should conduct spiked measurements at a rate of three per 100 measurements, with a minimum of three per year and a maximum of six per month.