text: instrument and errors due to position or lo- 
  cation of the installation. The instrument 
  error must be small by design of the equip- 
  ment and is usually negligible in equjpment 
  which is properly maintained and cared for. 
  The position error of the installation must 
  be small in the range of airspeeds involving 
  critical performance conditions. Position 
  errors are most usually confine,d to the static 
  source in 
  the actual static pressure 
  sensed at the static port may be different 
  from 
  free airstream static pressure. 
  When the .,aircraft is operated through a 
  large range’ of angles of attack, the static 
  varies ‘quite greatly 
  pressure distribution 
  to’minimize 
  and it becomes quite difficult 
  the static source error. 
  In most instances a 
  compensating group of static sources may 
  be combined to reduce the position error. 
  In order to appreciate the magnitude of this 
  problem, at flight speed near 100 knots a 
  
  that 
  
  the 