Question: How do I calculate error for averages?

I just installed the device indoor to check PM2.5 air quality in our flat and how the new air purifier works. After a while I am planning to move it outdoor.

As mentioned elsewhere I developed a micro service to notify me when readings cross a threshold. I have those values expressed as a range since we have the error range for the sensor.

PA-II comes with two PMS 5003 laser counters to estimate air particulate concentration. Specifications sheet among other things cite a maximum consistency error for PM2.5. This tells me the internal precision w/o reference to a true or known value. But what kind of distribution is assumed for this precision estimate? And what is the significance? As example I would have expected to read +-10% with a significance of 2.5 standard deviations for a normal distribution.

Without this piece of information I wouldn't know what probably range to assign and how to calculate the precision for averages between the two sensors and for different timeframes. Am I overthinking it and +-10% is just fine enough? Thanks.