Presumably someone does the ongoing calculation to determine the slowly-decaying energy of the Cs-137 source otherwise your rad monitor will appear to become more inaccurate...? Yes, I know it would take a long time; we've had the same Cs-137 for the last 28 years and it'll be around long after I'm gone...
They actually purchased a new GC made by Fluke recently as he old one was notoriously wayward.....not what you need where radiation is concerned.
