TM 1-1510-225-10 3C-14 (a)  Navigation  Displays.    The  navigation displays  are  selected  by  placing  the  rotary  switch  on the   control   unit   to   NAV.      In   this   mode,   Data   NAV enables data from two independent navigation sources, if available, and displays either or both on the indicator.    Additionally,   the  HSI's  OBS  knobs  can  be used  to  control  a  course  line  about  the  VOR  when selected from the control unit. The  current  magnetic  heading  of  the  aircraft  is displayed   on   a   scale   at   the   top   of   the   screen   to establish  a  visual  reference  point  for  pilot  orientation.   Selected heading can also be displayed graphically on the  indicator  when  HDG  is  activated  on  the  control unit. When the appropriate designator is selected, via the     control     unit,     the     active     VOR     establishes     a reference   point   for   the   designator.      The   designator controls    on    the    control    unit    will    then    move    the designator  symbol  to  any  point  on  or  off  the  screen within  approximately  423  nm  of  the  VOR  and  display the   radial   and   distance   to   the   designator   from   the VOR.  A solid line connects the designator   position to the VOR.  The homed designator position is the VOR. The designator can be selected to work with the VOR for either of the navigation sources via the  NAV 1 / NAV 2 slide-switch on the control unit.  Alphanumeric readout  of  radial  and  distance  of  the  designator  from the  VOR,  as  well  as  bearing  (magnetic)  and  distance to the designator from the aircraft, is displayed on the screen. The designator can be used to create a waypoint on  the  display  from  a  VOR  or  TACAN.    Since  the designator  is  fixed  geographically  relative  to  VOR,  it can   be   used   similar   to   a   waypoint,   although   not coupled to GDI. When     the HOME     button     is     pressed,     the designator  is  returned  to  the  VOR  and  the  readout  of distance  to  designator  and  radial  of  designator  with respect to VOR goes to zero. When  the  designator  is  activated  for  one  VOR and   then   the   other   VOR   selected,   the   system   will retain    the    data    for    the    first    navigation    source    in memory.  An asterisk in the color of the first navigation source  will  be  displayed  in  the  top  left    hand  of  the screen  to  the  right  of  the  Station-t o-Designator  (S-D) legend,  provided  that  data  on  the  position  of  the  first navigation   source   is   present.      This   asterisk   will   be removed when position data is lost. (b)  Graphic Displays. The graphic display   symbols   are   Superimposed   on   displays   of radar returns.  Refer to Figure 3C-8. Figure 3C-8.  Graphic Display Symbols 1    Ground     Station     Symbol.          The VORTAC  or  VOR/DME  symbol  is  accompanied  by  a readout  of  the  station  radial  and  ID,  displayed  in  the lower left portion of the display. 2    DESIGNATOR     SYMBOL.          The DESIGNATOR  SYMBOL  is  selected  to  work  with  the VOR for either station by the control unit. 3    Compass     Heading.     The     current magnetic   heading   of   the   aircraft   is   displayed   on   a scale   at   the   top   center   of   the   screen.   A   selected heading  line  may  also  be  displayed  by  pressing  the HDG switch on the Control Unit. 4    Course   Lines.    The  waypoint  and ground  station  symbol  course  lines  are  displayed  as solid  lines  through  the  symbols  and  originate  from  a position determined by the settings of the HSI(s)  OBS  knobs. 5    DES   NAV   1   /   DES   NAV  2  Slide Switch.    The  designator   IN  /  OUT and  RAD controls are  used  to  move  the  designator  symbol  to  any  point on  or  off  the  screen,  with  the  VOR  as  reference,  and display  radial  and  distance  to  the  designator  from  the VOR,  whether  or  not  the  VOR  station  is  within  radar range, as long as signals are being received.  The S-D readout  is  displayed  in  the  upper  left  portion  of  the display and the Aircraft-to-Designator (A -D) readout is displayed in the lower right portion  of the display.  With the designator in the home position, or positioned on the VOR, a tick is displayed to indicate the direction of OUT   movement.      This   tick   is   removed   once   the designator    is    moved    out    from    the    ground    station symbol.  A solid line connects the designator symbol to the VOR symbol.  By pressing the   HOME switch, the designator   is   positioned   on   the   VOR,   with   the   tick pointing to magnetic north. (3)   NAV Operation.