The machines were in an undisclosed location deep inside a Hershey chocolate mine.
The readings were 29.0 pCi/L versus 28.6 pCi/L for the suspect CRM
RPD = |(29.0 - 28.6)| ÷ (29.0 + 28.6) ÷ 2] x 100% = 1.4%
No anomalous data was observed. A difference of 0.4 pCi/L seems fairly insignificant, especially given the accuracy of machine is 25% or 1.0 pCi/L, whichever is higher after at least 24 hours of exposure.