The RuuviTags read an offset compared to all my other devices.
The breakout boards with BME280 are also lower, I tested one yesterday which was ok (-2% compared to another device which is within its tolerance).
But overall they are not at the same level to each other nor to other devices.
As mentioned earlier two RuuviTag show about the same reading in a box, while the third one is 4% lower.
For testing the breakout boards I use Esp32 development boards with firmware created with Esphome. I checked the calculations used and they are the same as yours, copied from the datasheet using the calibration values.
Maybe all my breakout boards are not so good, China stuff, but I assumed at least that the RuuviTags read about the same values within their tolerance which is not the case.
I tested all my SHTC3 breakout boards which just show the same values.
So overall for me the BME280 don‘t work at all. Or it could be all others are wrong and they are… I have no idea, as I also said I tried with saturated salt solution NaCl and the other devices have an offset to 75%, never reached that, but while all other read 72% -74% the RuuviTags are at 65%, the third one even lower.
I read the blog entry I linked, I read your blog post about testing but I can‘t get reliable results.
I have chemical clean NaCl and destilled water and a sealed glass where I can place the sensor directly over the solution but nothing in the range of 75%…