BMP085 barometric pressure off

I built the Weather from the book Arduino for Ham Radio. It works ok but my barometric pressure is off. Its is 1.10 mb low. Any ideas on how I can make it right Jim D

Add a constant offset.

These sensors are often calibrated for sea level @25C or so. The sensor doesn't know at which altitude you live ;)

It is performing within specifications, so just add 1.1 mbar.

robtillaart: Add a constant offset.

These sensors are often calibrated for sea level @25C or so. The sensor doesn't know at which altitude you live ;)

Another one of those constants eh? ;)

Sensors like the BMP085 are "absolute", meaning that they report the local air pressure. However, official weather stations and airports usually report the air pressure corrected to sea level. If you live above sea level, the sensor output will generally appear to be low compared to the reports.

You can fix this by either applying the correction to sea level (a power function of the altitude), see http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html or, add an empirically determined constant.