Air quality monitors: paying more does not get you more accuracy

I've been tracking air quality in Gary, IN for a few years now. It started with a PurpleAir ($), then a AQMesh pod ($$$$$) for a few months, now I'm rocking a Sensit RAMP ($$$). Just haven't spent too much time updating the dashboard I built to showcase the data: https://millerbeach.community. I had one sensor up and running at a time, so couldn't compare all 3 (PM only) against each other.

Indoors, I've been using a Canairi Air Quality Sensor, but that's just a simple CO2 monitor, along with my Dyson hot/cool air purifier.

I'm looking for a rough idea of what my family are breathing, I don't mind if numbers aren't 100% accurate (hopefully as small -/+ %, though).

Even the cheapest load cell is pretty damned accurate and the average between the four of them is going to be accurate within 0.1kg (~0.22lbs). Having said that, load cells have this problem where their values drift over time but only if there's a constant weight on them. If you step off the scale and allow it to re-calibrate itself (which is what it does every time it turns on) there will definitely not be enough drift to matter from a, "how much do I weigh?" standpoint. All it takes is like 2 seconds without weight for a load cell to "settle down" back to its not-actually-very-noisy resting position.

I've tested loads of the cheapest possible load cells money could buy along with some load cells I took from an expensive transparent scale that had cracked. They were all far more accurate than I was expecting and any differences between them was negligible.

The longer you wait before weighing something the less accurate it'll be but only by tiny, negligible amounts. Like, if you're weighing something that's 100kg and you waited ten minutes after calibration (something most scales won't allow because they all have something like a 30-second timeout) you'd still get a value that's within 0.01 of 100kg. They don't drift that much at rest unless there's some serious temperature variations or you had something resting on the scale the entire time.

It's because of how load cells (and scales) are manufactured. They're made for weight classes like 100g, 1kg, 2kg, 3kg, 5kg, 10kg, etc. So to make a scale for a particular weight you pick the load cells you'll need for the range you want.

Higher quality scales don't select higher quality load cells; they're all the same (reasonable quality) for the most part! Instead they just use more load cells and just take an average of all their values, multiplied by the number of cells, to measure weight.

So if you want a damned accurate industrial scale for measuring weights around 1kg you'd use like twelve 100g load cells rather than a single 2kg load cell or two 1kg load cells. Of course, then the hard part becomes, "how do I distribute this weight perfectly evenly across all of them?" so you have to take tolerances into account to make sure that at no point can weighing part of your scale rub against the side of its container or accidentally get something wedged between the scale part and the case.

There's loads of other things to consider as well but for the most part the accuracy of the scale is a factor of how many load cells its using, not the quality/manufacturing tolerances of the load cells themselves. Because even with the most precise manufacturing methods load cells will still drift and be impacted by temperature. All you can do is calibrate regularly, test them, and hope for the best (or use a completely different technology).