Hi AnnaB,
Thanks for your inquiry.
BMP280 has min/max absolute accuracy of +/-3hPa in the range from 300hPa to 1100hPa and from 0C to +65C. However, after soldering BMP280 on PCB there will be mechanical stress applied to BMP280 so that the offset may have changed. In order to get better accuracy you can do end-of-line calibration in your production line with a reference pressure meter. You can then save the offset of each BMP280 into the processor's flash memory and apply the offset to all future measurements. Then all your units will have accuracy within the typical range of +/-1hPa after end-of-line calibration.
Please see the attached "BST-BMP280-AN005-03_end_of_line_calibration.pdf" for more information.
Thanks.
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