# Should I add or subtract PA when calculating performance

I am planning a cross country and I wanted to know how would I calculate my PA for performance.

If the elevation of my airport is 16ft

and the altimeter setting for the day is 30.03

I subtract

30.03 -29.92

.11

.11*1000=110ft

Do I add the factor to Field elevation? or would I subtract?

and what determines if I add or subtract?

And if I am climbing to an altitude of 6000, would I use a Altitude OF 6000?

2.Should I add/subtract that PA factor TO to or from 6000 to get my PA?

• Alway subtract current altimeter setting from 29.92. 29.92 - 30.03 = -.11 * 1000 = -110 ft. If the pressure is lower, the subtraction would be positive, and you add the result to field elevation. Jul 31 at 3:45
• @wbeard52 Ok I got that but what I am trying to understand is why would we subtract the conversion factor or add it if it needed to be added. Just because its a negative number we subtract and add if its positive? whats the reasoning behind that theory? Jul 31 at 17:10
• If the altimeter setting is higher than 29.92 it would indicate that a given volume of air is at a lower altitude. so when we apply the formula above, we get a negative number so that the pressure altitude becomes lower than field elevation. Aug 1 at 0:05