Hello alll
I’m currently writing a paper about the measurings, that I’ve made with my Classic PA-II Sensors. In the description of the website it says, that the Sensor has two laser counters, which get compared to get a good measurand.
This information is a bit short. Can somebody please carry out the operation of the sensor a bit more, so I can write how this exactly works with these two laser counters?
Thank you for your help! 
Hi @Elia_Seitz
Classic PA-II sensors contain two PMS5003 laser counters. These counters conduct two independent measurements. When you look at the graph on the map for example, sensors with two laser counters will display 2 lines. If you look at the image below, you can see a black and a blue line.
These are the two different laser counters. The AQI score shown on the map is the average of these two values. Additionally, the two independent channel values can be pulled from the API using the “a” and “b” values.
Hi @Kieran_PurpleAir
Thank you very much for your response!
Did I understand this right?: When you download the data, the pm2.5_atm is the average value of the two laser counters (pm2.5_atm_a and pm2.5_atm_b).
Hi @Elia_Seitz
Yes, that is correct. The same goes for the pm2.5_cf_1 and pm2.5_alt categories. You can return the averaged results, or the two channels individually.