RPM - Revolutions

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 $--RPM,a,x,x.x,x.x,A*hh<CR><LF>

 Field Number: 
  1) Sourse, S = Shaft, E = Engine
  2) Engine or shaft number
  3) Speed, Revolutions per minute
  4) Propeller pitch, % of maximum, "-" means astern
  5) Status, A means data is valid
  6) Checksum