Here is a web link to help newbies in setting up the barometer on there station....


Could be worth making into a sticky thread


Altitude and Atmospheric Pressure

I think the way to work out the off set from the absolute pressure, is to use your nearest official stations reported pressure, which you can find on line. The problem is, that the stations report what the pressure was at a time in the past - the data is not current real time data.

Usually the updates are at either 20 past the hour or 10 to the hour and do seem to be quiet random. When attempting to calibrate the off set, log the data from your system at 20 past and 10 to, then keep checking the official station for updated data until you have a time match. From that you should be able to work out whether your Relative pressure needs to be adjusted up or down and by how much.

I use the data from United Kingdom Weather Forecast - Current weather in London, United Kingdom - Freemeteo.com

Has anyone found a better way to do the calibration?

I've used the Met office surface pressure chart which seems to be updated every 12hrs - midnight and noon. Probably best done when weather fairly settled and isobars well spread. If you look at several sites there can be a fair bit of variation.