TM 1-1510-225-10 3C-32 1.  Compare Annunciator (ACT) 2.  XFR/MEM Switch 3.  Frequency Select Knobs 4.  ACT Button 5.  TEST Button 6.  Light Sensor 7.  STO Button 8.  Volume Control 9.  Power and Mode Switch 10.   Annunciators (MEM, HLD) 11.   Preset Frequency Display 12.   Active Frequency Display Figure 3C-15.  CTL-32 NAV Control (6)   Light     Sensor. The built-in sensor automatically controls the display brightness. (7)   STO Button.  The  STO  button  allows  up to four preset frequencies to be selected and entered into    the    control's    memory.        After    presetting    the frequency  to  be  stored,  push  the  STO  button.    The upper     window     displays     the     channel     number     of available   memory   (CH   1   through   CH   4);   the   lower window   continues   to   display   the   frequency   to   be stored.  For approximately 5 seconds, the  MEM switch may be used to advance through the channel numbers without  changing  the  preset  display.    Push  the   STO button  a  second  time  to  commit  the  preset  frequency to memory in the selected location. After approximately   5   seconds,   the   control   will   return   to normal operation. (8)   Volume   Control.      A   volume   control   is concentric with the power and mode switch. (9)   Power and Mode Switch.  The power and mode  switch  contain  three  detented  positions.    The ON   and   OFF  positions  switch  system  power.    The HLD    position    allows    the    NAV    frequency    to    be changed,   but   holds   the   DME   to   the   current   active frequency. (10)   MEM  and  HLD  Annunciators.  The   NAV  control   contains    MEM    (memory)    and    HLD   (hold) annunciators.        The    MEM    annunciator    illuminates whenever a preset frequency is being displayed in the lower window.  The  HLD annunciator indicates that the DME   is   held   to   the   active   frequency   at   time   of selection;  the  NAV  frequency  may  be  changed.    The upper  window  now  displays  the  NAV  frequency  and the lower window displays the held DME frequency. (11)   Preset   Frequency   Display.    The  preset (inactive)    frequency    and    diagnostic   messages   are displayed in the lower window. (12)   Active   Frequency   Display.      The   active frequency, frequency to which the VIR-32 Receiver is tuned,  and  diagnostic  messages  are  displayed  in  the upper window. c.     Operating Procedures.  CAUTION It is not practical to provide monitoring for all    conceivable    system    failures.        It    is possible   that   erroneous   operation   could occur  without  a  fault  indication.    It  is  the responsibility of the pilot to detect such an occurrence by means of cross-checks with redundant or correlated information available in the cockpit.