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Thanks for your answer. 8542 39 00 does not seem to exist, so closest should be 8542 39 11. (See https://www.tariffnumber.com/2020/854239)   In the meantime, I also got an answer from Bosch customer support and here is their answer. Dear valued customer, thank you very much for your inquiry and your interest in our products. The tariff number for the BME280 is 90258080. However, if it is only the sensor for third-party components, we cannot make any recommendations. Best regards,   ... View more

In the end I found this page http://bmcnoldy.rsmas.miami.edu/Humidity.html So my method is given the temp and humidity returned by the sensor, to calculate the dewpoint, then add my correction offset to the temperature and then from this new temp and the dewpoint calculate the new humidity. static double compensate_temp(double t_mes, double t_comp, double rh) { double new_rh, td; // Calculate Td td = 243.04 * ( log(rh/100) + (17.625*t_mes)/(243.04+t_mes) ); td /= 17.625- log(rh/100) - (17.625*t_mes)/(243.04+t_mes); // Calculate new RH new_rh = 100 * exp((17.625*td) / (243.04+td)) / exp((17.625*t_comp)/(243.04+t_comp)); return new_rh; } Something like this above. On wiki, you can find some equivalent formula but with different coeff. Hope my method is valid...   ... View more

I found the issue and it was on my side. Following your first answer, I tried to use the field BSEC_INPUT_HEATSOURCE and discovered that I once used it in the past and left a hardcoded value of 3d in my call to bsec_iot_init(). Once fixed, temperature difference between sensors is less than 1d and humidity difference is in range of the +/- 3 % accuracy. Problem solved. Thanks for your support. But as I am using BME280 and need to add an offset to temperature (to report a correct temperature), what I still need to do is to estimate the RH with this offset temperature. I understood that for BME680, this is already supported with BSEC driver, but what about BME280 driver? I did not find anything for this. Would you have the formula to calculate this new RH? I found some on internet, but not sure they are valid.... Thanks.     ... View more

Thanks for the reply. I will try to do the calculation and see if I can get a correct humidity. I have a reference for temperature so I can tune temperature correctly. And by the way, from your answer I realized I did not compensate temperature correctly on BME680 as I am not using BSEC_INPUT_HEATSOURCE. But then what I don't understand is why I have some much differences in temperature. Same board, some place, same time and the I can have 4 degree difference between BME280 and BME680. The accuracy is given for +/-1d in normal temp range for both sensors. So in worst case I should expect 2d difference. What can I do to improve accuracy? Are there some cases which could degrade accuracy? Thanks.     ... View more