Bart Bailey wrote:
I show a difference between my local barometric reading and the sea
level reading (Lindbergh ATIS) of about .45".
What is the formula to calculate altitude based on this disparity?
I think my altitude here in North Park is about 350 ~ 400 feet.
(387 per the GPS)


It's an exponential equation, in geopotential meters (not even regular
meters). You're probably better off saying "close enough" and not
bothering to figure it out. You'll end up really frustrated (we had
this as a question on a synoptic exam in college, based on our 11-story
building).

However, if you still want I can look it up in my textbooks.