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I have a CO₂ sensor running in the shop, mostly to monitor peak CO₂ levels when folks are around. Somehow tho it never occurred to me to look at the troughs. The number never goes below 420 ppm. because that’s how much CO₂ is in the air now. that’s the most there’s ever been. https://twitter.com/aallan/status/1443676316000210950

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