Today I performed a data check on the sea level pressure values calculated from my mercury barometer.  During the month of December 2016 I recorded daily values of the mercury barometer sea level pressure and simultaneous National Weather Service values from O'Hare Airport and Midway Airport, near me here in Chicago.  The analysis shows that the data from O'Hare averages 1.5 mb higher than from my barometer.  The data from Midway averages 2.5 mb higher.  Several causes may explain this difference.  These are all presented on a new webpage, which may be found under 'Mercury Barometer Data Check', which is under 'Barometric Calculations' on the home page.

Go to 'Mercury Barometer Data Check'.