text: 0.05 psi position error is an airspeed error 
  of 10 knots. A typical variation of air- 
  speed system position error is illustrated in 
  figure 1.6. 
  
  (3) The equivalent airspeed (PAS) is the 
  result of correcting the (CAS) for compressi- 
  bility effects. At high 
  flight speeds the 
  stagnation pressure recovered in the pitot 
  tube is not representative of the airstream 
  dynamic pressure due to a magnification 
  by compressibility. Compressibility of the 
  airflow produces a stagnation pressure in 
  the pitot which is greater than if the flow 
  were incompressible. As a result, the air- 
  speed indication is given an erroneous mag- 
  nihcation. The standard airspeed indicator 
  is calibrated to read correct when at standard 
  sea level conditions and thus has a com- 
  pressibility correction appropriate for these 
  conditions. However, when the aircraft is 
  operating above standard sea level altitude, 