One of the 6 rules to forecasting excellent visibility that is stated in Brent Scudder's White Mountain Viewing Guide is: 6.)When a barometer (set for sea level) exceeds 30.20 inches at one or more of the following locations: Burlington, VT; Syracuse or Buffalo NY.

I've two questions. When a barometer reads 30.20" at sea level, what is the corresponding reading at the observatory?

Are there several locations for weather instruments at different elevations?