I live in Denver CO, and I have come across a mystery having to do with barometric pressure. If you go look at any weather site, like: http://www.wunderground.com/cgi-bin/findweather/getForecast?query=denver+co You will see the local pressure (at the time of this writing) is listed as 30.33 inches of Hg, which is 14.89 psi. However, I have a brand new certified absolute pressure transducer that shows the local pressure is 11.85 psi. Also, if you look at how pressure is supposed to vary with altitude, such as at this site: http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html You can verify that the predicted pressure at Denver (5300 ft elevation) is around 11.9 psi. This is much closer to the pressure I measured with the pressure transducer. The difference is small and can probably be explained away due to local variations, temperature and humidity effects, etc. But if you think this is a single anomaly, think again. I first noticed this in July when the weather was hot. I have observed this over and over the past few months in different conditions. The weather pages consistently give values around 29-31 inHg, which is far higher than I have ever measured with my PT. So my question is, why the difference?