# Stations with readings of 0

**URL:** <https://community.purpleair.com/t/stations-with-readings-of-0/8518>\
**Category:** API\
**Created:** [April 26, 2024, 7:38pm UTC](https://community.purpleair.com/t/stations-with-readings-of-0/8518 "2024-04-26T19:38:29Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Bat](https://avatars.discourse-cdn.com/v4/letter/b/7ba0ec/32.png) [@Bat](https://community.purpleair.com/u/Bat)\
**Post date:** [April 26, 2024, 7:38pm UTC](https://community.purpleair.com/t/stations-with-readings-of-0/8518/1 "2024-04-26T19:38:29Z")

</div>

Hi!

I’m relatively new here. Our team uses purple air APIs to fetch AQ data in the Mongolian region. We see some readings on the real time map that display 0 and after checking out individual sensor readings in the stations, they individually show vastly different readings, which I suspect then get aggregated to 0 because they can’t agree on a value.

My questions are:

1. What method do PA use to calibrate, aggregate different sensor readings into a singular station value?
2. Is there a way for us to directly fetch individual sensor readings?

---

<div class="post-metadata">

**Author:** ![Kieran](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/kieran/32/6220_2.png) [@Kieran](https://community.purpleair.com/u/Kieran)\
**Post date:** [April 27, 2024, 7:55pm UTC](https://community.purpleair.com/t/stations-with-readings-of-0/8518/2 "2024-04-27T19:55:55Z")

</div>

Hi @Bat

I’ll quickly say that the most common reason a sensor reads zero is that one of the channels has a broken fan.

1. On the PurpleAir map, readings for both of a sensor’s channels are averaged to produce the singular value. This is the same in the API, if you pull “pm2.5\_cf\_1,” for example, that field is averaging the pm2.5 data from both of that sensor’s channels.

2. You can retrieve data from individual channels in a sensor. Using the same example as above, instead of querying “pm2.5\_cf\_1,” you could pull both “pm2.5\_cf\_1\_a” and “pm2.5\_cf\_1\_b.” When you see “a” and “b” in the [API documentation](https://api.purpleair.com/), that is going to be the two individual channels in a device.