Good points IP, and I'd also add that punters should be aware of...

Good points IP, and I'd also add that punters should be aware of the difference between a spot XRF reading (targeted sampling of a 3mm radius) and a split assay (standardised sampling and analysis to represent average grade in a pre-determined length of core). Even when the guns are working properly we have witnessed plenty of dubious reporting of field XRF results at our beloved ASX casino.

But going back to Mett's suggestion in the opening post regarding temperature issues and BOA's faulty unit: With ambient temperature below about minus 20 degrees C, I understand they can be difficult to hold steady, and getting up around 400 degrees C, they become completely stuffed. Best to keep within -5 and 50.