TM  55-1510-221-10 b. Controls/Indicators and Functions (Pilot's HSI, fig. 3-10). (1.) Distance display. Provides digital dis- plays  of  DME/TACAN  or  INS  waypoint  distance. TACAN  distance  is  displayed  in  1/10  mile  incre- ments.  INS  distance  to  waypoint  is  displayed  in whole  mile  increments.  The  display  will  show  dashes when  the  distance  input  data  is  invalid  or  absent. (2.) Rotating heading (azimuth) dial. Dis- plays gyro stabilized magnetic compass information on a dial which rotates with the aircraft throughout 360  degrees.  The  azimuth  ring  is  graduated  in  5 degree  increments. (3.)  Lubber  line.  Fixed   heading   marks located at the fore (upper) and aft (lower) position. (4.)  HDG  flag.  Indicates  loss  of  reliable heading   information. (5.)  Heading  bug.  The  notched  orange heading  bug  is  positioned  on  the  rotating  heading dial by the heading knob, to select and display a pre- selected  compass  heading.  Once  set  to  the  desired heading, the heading bug maintains its position on the  heading  dial.  The  difference  between  the  bug and the fore (upper) lubber line index is the amount of heading select error applied to the flight director computer. In the heading mode the ADI will display the proper bank commands to turn to and maintain this  selected  heading. (6.)  Course  display.  Provides  a  digital readout of selected magnetic course. (7.)  Course  pointer.  The  yellow  course pointer  is  positioned  on  the  heading  dial  by  the remote  course  knob,  to  a  magnetic  bearing  that  coin- cides  with  the  selected  course  being  flown.  The course pointer rotates with the heading dial to pro- vide  a  continuous  readout  of  course  error  to  the computer. (8.)  Bearing  pointer.  Indicates  ADF  or NAV  relative  bearing  as  selected  by  the  bearing pointer source switch. (9.)  ADF  annunciator.  When   illuminated, indicates  ADF  bearing  information  is  being  dis- played. (10.)  Bearing  pointer  source  switch.  The bearing pointer source switch, located on the pilot’s HSI,  provides  for  selecting  between  ADF  or  NAV bearing  information  as  presented  by  the  bearing pointer.  Each  push  of  the  select  switch  alternates selection  of  ADF  or  NAV.  Upon  power-up  or  fol- lowing  long-term  power  interruption,  NAV  is  dis- played. 3-22 (1 I.) NAV annunciator. When illuminated, indicates  NAV  bearing  information  is  being  dis- played. (12.)  NAV  flag.  Indicates  loss  of  VOR, TACAN  or  INS  information,  or  unreliable  naviga- tion  signal. (13.)   Compass   synchronization   annuncia- tor. The compass synchronization annunciator con- sists of a dot and X symbol display. When the com- pass system is in the slaved mode, the display will oscillate between the dot and X symbol, indicating the heading dial is synchronized with a gyro stabi- lized  magnetic  heading. (14.)  Course  deviation  dots.  In  VOR  or TACAN  operation,  each  dot  represents  5  degree deviation from the centerline (± 10 degrees). In ILS operation,  each  dot  represents  1  degree  deviation from the centerline. In INS operation, each dot rep- resents  3.75  nautical  miles  deviation  from  center- line. (15.)  Aircraft  symbol.  The  fixed  miniature aircraft symbol corresponds to the longitudinal axis of  the  aircraft  and  lubber  line  markings.  The  symbol shows aircraft position and heading with respect to a radial course and the rotating heading (azimuth) dial. (16.) Course  deviation  bar.  The  course  devi- ation  bar  represents  the  centerline  of  the  selected VOR,  TACAN,  INS  or  localizer  course.  The  minia- ture  aircraft  symbol  pictorially  shows  actual  aircraft position in relation to this selected course. (I 7.) VERT flag. Covers  glide  slope  pointer when not receiving glide slope information. (18.)  Glide  slope  pointer/scale.  The  glide slope  pointer  displays  glide  slope  deviation.  The pointer is in view only when tuned to a localizer fre- quency. If the aircraft is below glide slope path, the pointer is displayed upward on the scale. Each dot on  the  scale  represents  approximately  0.4  degree  dis- placement. (19.) To-from pointer. The to-from pointers aligned  on  the  course  pointer,  are  located  180 degrees apart. One always points in the direction of the  station,  along  the  selected  VOR  radial  or towards the INS waypoint. (20.)  Navigation  source  annunciators.  Five different  annunciators  display  navigation  data sources.  They  are:  TAC  for  TACAN,  GPS  (not used), INS, NV2 for VOR 2, NV1 for VOR 1. WPT indicates arrival at INS waypoint. (21.) Course knob (located on the pedestal). Positions the course pointer.