
  SonMag is an acronym for Sonar-Magnetometer. This instrument provides
  the functions of a searchlight Sonar and a magnetic anomaly detector
  (Magnetometer). To invoke the Sonar, press 's' or click the SONAR panel
  button. The "crt" screen will will be marked in two ways: in the horiz-
  ontal direction, the sonar will give you a line showing the proximity of
  any shorelines. At the same time, the sonar will also be taking a
  vertical reading, infinitely drawing a pattern if it "sees" anything
  in the water below. Pressing 'd' or clicking the DATA panel button tells
  you, from top to bottom, your Latitude, the distance from any landmass 
  that the Sonar can detect, and your Longitude, (also the directions
  N,S,E,W). To start a Magnetometer paper reading, press 'm' or click the
  MAGNET panel button. A paper feed will come out of the slot on the lower
  right hand corner. If the contents of the Ocean below have one of the
  following characteristics, the Magnetometer output will be amplified
  peak-to-peak: 1) high concentration of magnetic ore in the ocean floor
  sediment, 2) a magnetic anomaly or diametrically opposed magnetic field
  such as is found at ocean ridges, or 3) a concentration of metal or
  magnetic rock at a relatively small distance. The data when in
  Magnetometer mode tells you the Latitude/Longitude range of the attempted
  readings, and a +(top of "crt") and -(bottom of "crt") number called the
  gamma: a positive gamma indicating the amplitude of anomaly of rocks
  magnetised in a field the same as the Earths current field and a negative
  indicating negative nomaly amplitude for rocks with a reversed field. 
  The buttons:
  DATA    Overlay Data for Sonar Mode or Magnetometer Mode.
          Keypress 'd'.
  SONAR   Toggle Sonar Mode.
          Keypress 's'.
  MAGNET  Toggle Magnetometer mode, start a paper reading.
          Keypress 'm'.
  COLOR   Change color of Sonar sweeps.
          Keypress 'c'.
  EXIT    Back to instrument room.
          Keypress 'e'.






