sufficient to cause the display to change one digit. For all other conditions, the deep, 4-499 ft.  range on the No.    550  will  yield  adequate  resolution.    The  resultant display   will   tend   to   appear   more   stable   because   a greater   change   in   depth   is   required   to   change   the reading.  In addition, the No.  550's transmit pulse width is increased significantly on the "deep" range to improve maximum  depth  capability  and  depth  reading  stability. This  takes  place  with  some  sacrifice  in  shallow  water (minimum   depth)   resolution,   and   is   why   the   2-99   ft. range  should  be  used  whenever  navigating  in  shallow areas. 6.  SET THE UPDATE RATE The   update   rate   on   the   model   No.      530   is   fixed   at approximately one sounding per second.  The model No. 540    digital    remote    automatically    is    adjusted    to    the update rate of the master unit to which it is connected.  It will  vary  from  a  minimum  of  about  0.4  sec.    when  used with  a  flasher  depthfinder,  such  as  Aqua  Meter's  NO. 374 "Cheater" 0-40 ft. model, to a maximum that is equal to the master unit's rate. The No.  550 is equipped with a front panel switch to set the  update  rate  or  the  speed  at  which  the  information displayed   on   the   LCD   readout   is   updated   with   new information.    In  the  normal,  down,  fast,  position  of  this switch, the displayed information is updated approximately  twice  each  second.    In  the  slow  position, the  displayed  information  is  updated  about  once  every two seconds.  The fast rate should be used, not only for normal operation, but also especially when navigating in dangerous   areas.      The   slow   rate   can   be   used   while cruising  in  known  areas  or  rough  waters.    It  will  yield  a more-steady,  and  easy-to-read  display.    The  slow  rate also  is  advisable  when  fishfinding,  since  the  fish  depth will be displayed for a longer period of time. 7.    SET  THE  SHALLOW  ALARM  (Also  see  "Quick Tuning", Pgs.  3 & 4) All  three  Aqua  Probe  digital  instruments  are  equipped with a variable SHALLOW WATER ALARM circuit.  This circuit  sounds  an  audible  alarm  whenever  the  boat  is navigated    into    an    area    where    the    water    depth    is SHALLOWER  than  the  alarm  setting.    This  means  you can  use  the  shallow  alarm  as  a  safety  device  to  help avoid  running  aground.    The  shallow  alarm  also  can  be used  as  a  navigational  tool  to  give  you  notice  when  a bottom   contour   line   on   your   marine   chart   has   been reached.  The shallow alarm can function very effectively too   as   a   fish   detector,   if   the   sensitivity   is   increased slightly    more    than    that    required    for    normal    bottom readings. There  are  two  switches,  plus  a  variable  knob,  used  to activate and adjust the shallow alarm circuit.  These are:   the alarm ON-OFF switch;   the  alarm  knob  which  is  used  to  adjust  the  shallow alarm   circuit   to   any   desired   alarm   depth   within   its range.   the  ALARM  SET/DEPTH  switch  which  is  basically  a DISPLAY  SWITCH.    It  selects  what  information  is  to be displayed on the LCD readout.  When in the normal down or DEPTH position, the LCD will show the depth of water below the transducer.  When this switch is in the up, or ALARM SET, position, the LCD readout will show the depth to which the alarm circuit is set. Turn   on   and   adjust   the   unit   for   normal   operation   as described earlier.  At this point, the correct depth should be displayed on the LCD readout. Move  the  shallow  alarm  ON-OFF  switch  up  to  the  ON position.    Note:  At  this  point  the  Audible  Alarm  should not be heard since the shallow alarm knob was preset to minimum.      The   alarm   may   sound   when   the   alarm   is turned   on   if   the   depth   is   shallower   than   that   alarm setting.  Keep in mind that whenever this switch is to the ON    position,    the    shallow    alarm    circuit    is    activated regardless    of    the    position    of    the    display    (ALARM SET/DEPTH) switch. The  LCD  readout  still  should  be  indicating  the  depth  of water.    Now,  move  the  DISPLAY  switch  from  the  down DEPTH position to the up ALARM SET position.  At this point  the  LCD  readout  will  indicate  the  depth  to  which the shallow alarm is set. Slowly   rotate   the   shallow   alarm   knob   to   increase   the depth to which the alarm 12