A:Answer I'm not an expert but I think the bigger number is the unit's estimation of particles moved and the smaller number is the type of the particulate matter (e.g. PM2.5, PM0.1, PM10).
Honestly, i don't pay too much attention on this as it fluctuates during its run anyway and it all depends on the current condition of your room.
As long as it turns from RED to GREEN, I trust that the air is 'cleaner'. As to whether that's really accurate or not, I am also not sure. I guess I'll find out during our wildfire season to put it to a more 'realistic' test.
