4.  SET THE RANGE Each  of  the  Aqua  Probe  digital  depthfinders  will  operate  over  a  depth  range  unique  to  that  particular  model  as follows: Model Min.  Operating Depth Max.  Depth No.  530 3' 400' + No.  540 See 4A.  below No.  550 (Shallow Range) 1.9' 99.9' + See 4B.  below (Deep Range) 4' 500' + 4A.  NO.  540 RANGE While most operation instructions, which apply to the No. 530  and  No.    550  digital  depthfinders,  also  apply  to  the No.  540 remote, it is well to remember that the No.  540 only samples the signals of its the main depthfinder. Therefore, the minimum depth capability of the No.  540 remote   is   determined   primarily   by   the   transmit   pulse width of the master depthfinder to which it is connected. The minimum depth rating usually will be the same (plus 1 digit) as the master depthfinder.  As an example, if the No.    540  is  operated  in  conjunction  with  No.    530  that has  a  minimum  depth  capability  of  two  to  three  ft.,  the No.  540 will read as shallow as three to four ft. The  maximum  depth  capability  of  the  No.    540  remote also  is  determined  by  the  master  depthfinder.    In  this case,  the  factors  involved  are  the  transmit  power  and update  rate  of  the  master  unit.    As  an  example.    if  the No.  540 is used with an Aqua Probe No.  374 "Cheater" 0-40  ft.    flasher  type  depthfinder,  the  maximum  depth capability of the No.  540 also will be 40 ft.  When used with a No.  530 or No.  550 digital, the No.  540 will have the  same  maximum  depth  capability  as  the  master.    If another    brand    depthfinder    is    used    as    the    master, generally  the  No.    540  will  read  at  least  as  deep  as  the main unit. 48.  OVER RANGE CAPABILITY The model 550 can be read deeper than 99.9 ft.  on the shallow range.  When 100 ft.  depth is reached the "Over Range"  indication  will  be  displayed  above  the logo on  the  left  side  of  the  LCD.    In  this  case,  the  last  three significant  digits  of  the  depth  reading  will  continue  to  be displayed,  such  as  "07.4".    When  this  occurs,  it  will  not be   known   whether   the   true   depth   is   107.4.   207.4,   or 307.4 ft. True depth can be determined by momentarily switching to the deep range.  If "207" is displayed, the true depth is 207.4  ft.    In  this  way  0.1  ft.  resolution  can  be  achieved well beyond 99.9 ft.  - The  maximum  depth  capability  of  the  No.    550's  deep range is limited, by the digital processor circuitry, to 511 ft.,   when   the   update   switch   is   in   the   fast   position. Greater  depths  can  be  read  by  switching  to  the  slow update rate. 5.  READ DEPTH On the No.  530, 540 and on the deep (4'-499') range of the  No.    550,  the  depth  indicated  on  the  LCD  is  in  feet. The actual depth will be rounded-off to the -nearest foot by the digital processor.  Accordingly, an actual depth of 34.4 ft. will read 34.  ft.  If the actual depth were 34.5 ft., the  reading  would  be  35.    The  unit  will  read  34  ft  from 33.5 thru 34.4 and then 35 ft from 34.5 thru 35.4, and so on. When  the  depth  range  switch  on  the  model  No.    550  is moved  up  to  the  2-99  ft.    position,  a  decimal  point  will appear on the LCD and the unit will indicate the depth in tenth-of-a-foot  increments  with  0.1  ft.    resolution.    This "shallow"   (tenths-of-a-ft)   range   should   be   used   when very  good  depth  resolution  is  required,  such  as  when navigating  over  an  area  where  the  bottom  has  a  very gradually  changing  slope.    This  range  also  should  be used  when  you  are  in  extremely  shallow  water,  and  for all other applications requiring precise depth measurement.      Keep   in   mind,   however,   that   in   the shallow    range    the    depth    reading    will    vary    almost continually.    It  will  rarely  stay  the  same  for  more  than  a few seconds, even with the boat seemingly at rest.  This is because less than a one-inch change in depth is 11