def hPa_to_m(p):
      """
      Compute pressure altitude
      :param p: pressure (hPa)
      :return: altitude (ft) 
      """
      # https://www.weather.gov/media/epz/wxcalc/pressureAltitude.pdf
      return (0.3048*145366.45)*(1 - (p/1013.25)**0.190284)