Duplicate Measurements
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These are made by exposing two or more detectors side by side to the same conditions to see how much they differ. Duplicate measurements provide a way to estimate the reproducibility of measurement techniques and determine precision. The following table lists acceptable precision errors between duplicate (side-by-side) measurements for different devices:
| Measurement Device | Precision Estimate |
| Charcoal canister | less than 10% |
| Continuous radon monitor | less than 10% |
| Electret ion chambers | less than 10% |
| Continuous WL monitor | less than 10% |
| Alpha track detectors | less than 20%, dependent on total area analyzed |
| Grab samples | less than 30% |
The analysis of data from duplicates should follow the methodology outlined in EPA Radon & RDP Measurement Device Protocol, Goldin Section 5.3 1984/1992c. If the precision estimated by the user is not within the precision expected of the measurement method, the problem should be reported to the analysis laboratory and the cause investigated.