# Pure air II non sd. Which sensor is A?

**URL:** <https://community.purpleair.com/t/pure-air-ii-non-sd-which-sensor-is-a/526>\
**Category:** Troubleshooting\
**Created:** [April 24, 2022, 10:14pm UTC](https://community.purpleair.com/t/pure-air-ii-non-sd-which-sensor-is-a/526 "2022-04-24T22:14:56Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Eric](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/eric/32/406_2.png) [@Eric](https://community.purpleair.com/u/Eric)\
**Post date:** [April 24, 2022, 10:14pm UTC](https://community.purpleair.com/t/pure-air-ii-non-sd-which-sensor-is-a/526/1 "2022-04-24T22:14:56Z")

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Sensor A has only 8 percent confidence so I need to clean it out. Which side is A and which is B (compared to the USB plug). (in case I try compressed air)

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**Author:** ![Doug\_PurpleAir](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Doug\_PurpleAir](https://community.purpleair.com/u/Doug_PurpleAir)\
**Post date:** [April 25, 2022, 8:20pm UTC](https://community.purpleair.com/t/pure-air-ii-non-sd-which-sensor-is-a/526/2 "2022-04-25T20:20:43Z")

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For the PA-II, PA-II-SD, and PA-II-FLEX, the side with the USB plug is channel B.