We can look at two areas of vastly different altitudes (Death Valley, CA, and Denver, CO) and notice that the barometric pressure is pretty close to the same. That seems odd because the latter should have far less pressure than the former because there isn’t as much air pushing down on an area well above sea level. Below sea level, there is a lot more air exerting pressure on everything below.

The truth is that regional barometric pressures are normalized to sea level. So, the normalization makes the reported barometric pressure of Death Valley and Denver similar (even though the actual pressures are very different).

In reality, the barometric pressure of Denver is around 24.7”Hg, which translates to around 12.1 PSIA (compared to the 14.7 PSIA or 29.92”Hg at sea level). Thus, using barometric pressure to calibrate tools is difficult and unreliable, and you must either do the math or consult a chart to convert normalized pressure readings into accurate ones.