is   set.      Notice   that,   as   the   control   is   advanced,   the number  displayed  on  the  LCD  readout  becomes  larger indicating   that   the   shallow   alarm   set   point   is   getting deeper. Once   the   shallow   alarm   has   been   set   to   the   desired alarm depth, move the DISPLAY switch down to DEPTH to resume reading the water depth on the LCD readout. You can check the alarm setting anytime the alarm is on by  momentarily  moving  the  DISPLAY  switch  to  ALARM SET. The   range   of   depth   settings   possible   for   the   Shallow Alarm varies from model to model as follows: Model Typical Range 530 5' - 100' 540 5' - 100' 550 2.5' - 50' CAUTION:  On  the  No.    550  digital  depthfinder  the shallow alarm has been designed to take advantage of     the     unit's     very-shallow-water     resolution     by allowing   the   alarm   to   be   adjustable   down   to   a similarly very-shallow depth.  Because of this it may be possible to adjust the No. 550's shallow alarm to a  set  point  that  is  shallower  than  the  No.    550  can read in the deep range.  When navigating and using the   shallow   alarm   in   very   shallow   areas,   always switch the No.  550 to the tenths (2' - 99') range. Please note that if the display switch is moved to "Alarm Set"  before  the  alarm  is  turned  on,  the  LCD  readout  will lock   onto   the   last   depth   reading.      It   will   continue   to display that same number until, either the alarm is turned on, or the display switch is returned to "depth". 8.      USE   THE   SHALLOW   ALARM   (See   Pg.   14   for "Anchor Alarm") This  section  deals  with  the  various  uses  for  the  shallow alarm.      They   include   safety   from   grounding,   use   for navigation  and  fish  finding.    The  section  in  this  manual on   "Navigating   and   Piloting"   will   detail   that   aspect   of depthfinder  use  very  thoroughly.    The  use  of  a  Shallow Alarm  as  an  aid  to  position  determination  and  following contours will become obvious. When  you  are  using  the  alarm  as  a  grounding  warning, the shallow alarm should be set to a depth that not only will  allow  adequate  clearance  below  the  hull,  but  also sufficient  advance  warning  that  a  dangerously  shallow area is being approached.  If the chart indicates that the depth  of  a  channel  nominally  varies  between  five  and eight  ft.    at  dead  low  tide,  and  abruptly  shoals  at  the edge,   adjust   the   shallow   alarm   just   slightly   shallower than  the  five  ft.    point.    This  will  give  you  the  earliest possible   warning   that   you   are   approaching   a   channel edge.      Always   keep   in   mind   that   the   depth   reading display   on   the   LCD   readout   is   the   depth   from   the transducer face to the bottom. To  use  the  Shallow  Alarm  as  a  fish  finder,  adjust  the setting  to  a  point  just  above  the  bottom,  so  that  any return  echo  between  the  surface  and  bottom  will  cause the  alarm  to  sound.    Then  advance  the  SENSITIVITY knob    to    three    or    four    graduations    higher    than    the threshold  point.    This  will  increase  the  sensitivity  of  the unit   so   that   it   will   respond,   not   only   to   the   stronger bottom  echo,  but  also  the  weaker  echo  signal  reflected from     fish.          When     the     alarm     sounds,     note     the instantaneous depth reading.  It will indicate the depth of the  fish  for  several  seconds,  then  resume  indicating  the bottom depth. 9.  SET THE DEEP ALARM The No.  550 also is equipped with a deep alarm that is fully adjustable from the front panel, much the same way as    the    shallow    alarm.        Accordingly,    its    operation procedure is very similar.  Turn on and adjust the unit for normal  operation  in  the  feet  range,  and  either  fast  or slow update rate.  At this point the correct depth should be displayed on the LCD readout. If  the  shallow  alarm  has  been  activated,  TURN  IT  OFF before   proceeding   with   the   adjustment   of   the   deep alarm.    Although  both  shallow  and  deep  alarm  can  be operated simultaneously, as will be described later,  they must be adjusted individually. Move   the   deep   alarm   ON-OFF   switch   up   to   the   ON position.  Note: At this point the audible alarm will not be heard    unless    the    water    depth    is    greater    than    the maximum deep alarm setting. 13