My Shelly Gas LPG has reported values of 0 ppm and occasionally 600 ppm. The threshold for a low alarm is 1800 ppm and 3000 ppm for high alarm. I suspect the device only measures in 600 ppm increments. If so, the low and high alarms would trigger at 3 and 5 increments, not much discrimination.
Has anyone seen a ppm value that is not a multiple of 600?