When was the last time you had that sensor calibrated properly with a can of test gas and a multimeter?

colechristensen an hour ago | parent [-]

Take it outside, as long as it measures 400-450 it's probably good.

Metrology calibration is necessary if you want accuracy better than 10%, but most of us don't care at all about that, instead we care about increments of 200ppm or more.

	▲	ShinyLeftPad a few seconds ago \| parent [-]
		There's local factors that can make it 200ppm. If you're near a busy road with not a lot of wind 600 ppm is possible. But I think it's not that important if you open your window at 1000 ppm or 1200 ppm