Niko,
I wrote to them about that today, because while all of the other data is pretty representative, the barometer is way way off (i.e. reporting 29.83 when it should be around 30.30 in/Hg). They said there are three options. One is to let it finish its 14-day learning period to see if it re-adjusts. Second, they said a learning period of 33 days is actually better, because the calibration algorithm runs for 4000 12-minute samples or approximately 33.3333333 days. However, they said the best way is to find a day when the pressure is around 29.92, pull out the batteries to reset and put them back in, then it should be pretty close to right. Seems like a strange way to calibrate an instrument to me. I suggested that they add a method to calibrate temperature/wind/pressure data in the acu-link software, before shipping it to Weather Underground, or let us calibrate within the console, which I believe you can for temperature and humidity. Overall, I'm pretty pleased with the system, except for the pressure readings, and no ability to link with any third-party software and having Weather Underground uploads limited to 15 minutes.
Hope this helps,
Chris