# Contradictory cf Information in API Docs

**URL:** <https://community.purpleair.com/t/contradictory-cf-information-in-api-docs/9827>\
**Category:** API\
**Created:** [August 11, 2024, 8:04pm UTC](https://community.purpleair.com/t/contradictory-cf-information-in-api-docs/9827 "2024-08-11T20:04:32Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Sina\_Hasheminassab](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/sina_hasheminassab/32/832_2.png) [@Sina\_Hasheminassab](https://community.purpleair.com/u/Sina_Hasheminassab)\
**Post date:** [August 11, 2024, 8:04pm UTC](https://community.purpleair.com/t/contradictory-cf-information-in-api-docs/9827/1 "2024-08-11T20:04:32Z")

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I find the information about cf=1 and cf=atm in the API documentation confusing. In one section, it says “pm2.5\_a returns channel A. This is equivalent to **pm2.5\_atm\_a** for sensors registered as **indoor** , and **pm2.5\_cf\_1\_a** for sensors registered as **outdoor**.” However, another section states, “Simple running averages are calculated using the **CF=1** data variant for **indoor** sensors and the **ATM** variant for **outdoor** sensors.” These two statements contradict each other regarding which CF is used for indoor versus outdoor sensors.

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**Author:** ![Andrew](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/andrew/32/1211_2.png) [@Andrew](https://community.purpleair.com/u/Andrew)\
**Post date:** [June 17, 2025, 9:12pm UTC](https://community.purpleair.com/t/contradictory-cf-information-in-api-docs/9827/2 "2025-06-17T21:12:42Z")

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This was a typo and has been fixed. Any PM field that doesn’t allow formula selection will default to:

- CF1 data for indoor sensors
- ATM data for outdoor sensors