Actually the real accuracy is much better, especially with optical NDIR sensors.

We do a lot of testing against reference grade sensors and typically see very good performance and reproducibility [1].

[1] https://www.airgradient.com/blog/performance-of-low-cost-co2...

That’s if the voltage supply was stable and within electrical specs for a sufficient period of time. We can see this is a snippet 2 hours into the discontinous collection.

3.6V is the maximum value that the nrf52832 SoC can handle. I would suspect the VDD is variable.