You may be correct. The thought that they didn't last for ever never cross my mind until now. Perhaps it's time to get it serviced.
Originally Posted by Kirk Keyes
But. It does have user-calibration setting on the back. This is used to zero-set it.
And then. If it is out of calibration then that does not necessarily explain why the two readings differ. The sensor is the same one but in one case uses a diffusion cone and in the other not. Would this meter be sophisticated enough to have two separate calibrations, one for each mode of use?