We'll ignore modern high-tech electronic barometers, such as those embedded in smart phones, etc. Most barometers of 'our vintage'  - though the dials may read in Inches Hg, along with millibars, etc. - are coiled Bernoulli tubes, and are mechanically adjustable to convert 'local' normal barometric readout to a sea-level equivalent - why? Just so that the pointer lines up more or less with the RAIN - CHANGE - FAIR regions on the dial!. 

I live in Tucson at ~2,600 ft elev, so my local normal is ~ 27.50" Hg or so - without adjustment I'd always reside in the 'rain - change' regions of the dial. 

If you're a pilot, you adjust your altimeter (same mechanical basics as your home barometer) to local pressure at ground level in order to yield your altitude above ground level when flying into and out of higher elevation fields.

For obvious reasons we were well versed in barometric theory, amongst all the other physics to do with flight. and you can bet your bippy I treated the process just as seriously as I took BESS, and my initial submarine qualification, and the requals on new-to-me boats. 

Both those qualifications left imprints on my brain ... some of which can be summoned up still, lol.

The combined quals let me relate the altimeter setting, versus the drop in inches of Hg barometric pressure when a couple of FB's running full bore for battery charge get cutoff from outside air; a very rapid 'rise' from sea-level to something a little higher than Denver - you bet some ears are gonna pop! It's about like being sucked into the core of a tornado (reliable pressure drop records in the -5" to -6"Hg range).