PRESTON PRESSURE PS-500 User And Maintenance Manual page 16

8. Now the display will show
XXX
In YY 
Where XXX is the sensed altitude and YY is the internal correction factor currently
stored in the calibration memory.
Using the pneumatics of the PS-500 or an attached pressure standard, go to a
pressure of 0 feet (referenced from 29.92 inHg), as read from the pressure standard.
When the altitude is stable for approximately 30 seconds, note the altitude displayed
on the PS-500 display in calibration mode.
If the displayed altitude is higher or lower than the standard, press the Exit or Leak
Check button as needed to incrementally change the altitude to be equivalent to the
standard.
As the altitude is adjusted, note that the displayed correction factor also changes. Use
this to fine-tune the altitude as close as you can to the standard.
When the PS-500 altitude matches the standard as close as possible, wait another 30
seconds to ensure that the internal mathematical filtering corrections have been done.
If satisfied with the results, press the Units button to proceed to the next calibration
level.
Note: Allowable error tolerances are as follows (these are the allowable errors per
AC43 Appendix E, not the accuracy of the PS-500):
Altitude
-1000
0
500
1000
1500
2000
3000
4000
6000
8000
10000
12000
Note: Make a written note of each calibration correction value. In the very rare
case that a calibration factor is lost from the memory, it can be re-programmed
without a complete calibration procedure. The correction values can also serve as a
+/-Error
5
5
5
5
6
7
7
8
10
15
20
22
Altitude
14000
16000
18000
20000
22000
25000
30000
35000
40000
+/-Error
25
27
30
32
35
38
45
51
57
15