Hi Pasha,
USA uses sea level and Canada probably does.
The average person in the USA is seeing the sea level pressure.
Someone in outdoor sports would be interested in both pressure readings.
I was surfing the web looking for countries that use elevation for barometric pressure.
The only thing that I have found is that sea level is used so that the entire world has a comparison.
I like your thought about Denver.
Ivan and you drove across the USA from Chicago to St. Louis to California.
You know how flat the mid section of the USA is.
This area is known as Tornado Alley.
Barometric pressure is very important there.
A sudden drop in pressure could mean a tornado.
So the use of sea level pressure is very important.
I live right where the mountains along the East Coast start.
If I would do some mountain climbing, the elevation air pressure is very important.
But I only need this information when I am going to do a particular sport.
When I am comparing Mansfield to Leiden, Vienna, and Saint Petersburg sea level pressure is the way to compare.
You need to show sea level pressure but have a way for someone to see air pressure at an elevation.
Showing the elevation would also be good.
Hopefully these can be done in a tooltip.
Marty