This is not a joke, I am really asking: how do you measure the accuracy of an air quality monitor? Comparing it to another monitor? Creating an air pollution condition and seeing how close to that is the measurement?
By the time the device lands in landfill, it probably won't ever have been too far off. And if the CO2 curve derivative starts to underperform and risk your deployed calibrations, throw some dollars an some anti-nuclear campaigns as that's cheaper than doing an update!
My Aranet4 was more like 1000 ppm off before putting it outside for awhile, despite being labeled as calibrated from the factory. It was going absolutely ballistic thinking my apartment was full of smog. After sitting outside to get a taste of ambient air, suddenly the inside of my apartment was fine.
You watch the readings go up and down as you close windows and cook and then open windows and let the fresh air in. You'll watch CO2 go up to 1200 and then back down to 500. Or PM2.5 go from 2 to 25 and back.
They're big changes that obviously correlate in logical ways with what is happening in your home.
And then it's really the relative changes you're watching. Even if values are off by 20% it doesn't really matter a ton for private personal use.
Because you're really just learning what the baseline values are for fresh air, how quickly values grow, and therefore when you prefer to open some windows. (Or this week, close them.)