@vreihen, thanks for the comments!
Are you talking about the BMP180? Because the 280 do have humidity.
I think sensor placement is obvious - if it's in a sealed case, pressure does not make sense, if it's in a case getting warm, temperature does not make sense.
How exactly did you calibrate it? In order to calibrate accurately the sensors need linear response, otherwise it's getting complicated.
And last but not least: Do you know any better or even calibrated (with certificate) sensors?