@Meditation guide The sensor in the meter uses chemical compound to detect CO and it will deplete fast in very high CO concentrations.
I believe the professional meters also use similar electrochemical sensors but of course better ones.
I have mentioned before I had an old meter(test 327 gas analyzer) and it died, because of CO exposure, the cells needed replacing.so it can be fixed. I have a new meter(kane 458) though that switches off the pump, if high CO is sensed.
You should always purge your meter after testing for CO aswell.
Do the meters need to be calibrated regularly and if so why?
yes, once a year. for a gas analyser To make sure they are reading the gasses correctly i imagine. like i use mine to test gas boilers, it needs to be reading correctly in order for me to be sure a boiler is safe.
The gas analyser tests for other things, as well as CO. every 5 years i have to have the cells changed in mine. I imagine it can depend on use though aswell