Calibrating co2 sensor

today i decided to recalibrate the co2 sensor on my pulse pro so i took the unit outside along with some other sensors that also measure co2 the other sensors were reading 350 ppm when we were outside unfortunately the ios app didnt allow me to select anything below 400 ppm for the reference point when calibrating i really should be able to select 350 as the reference point if im confident thats what it is. this should be changed.

While I agree that having a limit on calibration values is nonsensical unless it is a technical limitation, it’s also very unlikely that the sensors saying 350 are correct.

Prior to 1986, global co2 was around 350 so devices often self calibrated to 350 when the method of calibration was to put them outside. That didn’t mean it really was 350, it just meant it was a best guess. Unfortunately when it comes to co2 calibration, without complex equipment we are forced to calibrate to a best guess. The most convenient relatively accurate guess we have is any place outside away from sources of co2, then using the currently published global co2 average (which as of this comment is 416ppm).

I personally use a combination of outside calibration along with multiple sensors to get an agreement, and I give weight to more recently purchased equipment. For instance, my Titan controllers are horribly inaccurate and extremely sensitive to going out of calibration, while my pulse and Ecowitt devices are much more consistent and seemingly accurate. I don’t even bother to calibrate my Titans to outside; instead I calibrate all my Pulses and Ecowitt monitors outside, then bring them into a room with CO2 at an elevated value and use the best agreement from the calibrated devices to them calibrate my titans at the most common enrichment level (like 1250ppm). That way they are most accurate at the level I’m trying to target.

But yeah, why would they prevent us from calibrating at any value we choose; maybe Pulse can speak up about a limitation in the math or the sensor they use.