I'll let more knowlegable software types comment on your sketch. However it doesn't seem correct to have two variables used both named pressure, one a int and global in scope and the other defined as a automatic variable inside loop() as a long variable and then both used in the same expression:
long pressure = 950 + pressure / 8.5; //convert it to milli bars
I'm suprized that doesn't generate some kind of compiler error, but again I'd rather a software guru type comment on that.
Lefty