TM 55-1510-219-10 caused by continuous or inter- mittent condition.  Intermittent conditions light lamp until reset by TEST switch.  If continuous condition does not degrade atti- tude operation, lamp goes out when mode selector is set to ATT. Keyboard Consists of 10 keys for entering load data into data and FROM- TO displays. "N", "S", "E", and "W" (on keys 2,8,6 and 4) indicate direction  of  latitude  and  longitude.    TAC  and  DISP  (on keys "7" and "9") enable loading and display of TACAN station  data.    MV  and  DISP  (on  keys  "3"  and  "9")  are associated     with     loading     and     display     of     Magnetic Variation  and  Magnetic  Heading.    GRID  and  DISP  (on keys "5" and "9") are associated with loading and display of UTM coefficients. CLEAR key When  pressed, illuminates and erases data loaded into data dis- plays or FROM-TO display. Used to cancel erroneous data. After clearing, data loading can be resumed. WYPT CHG key When pressed, enables  numbers in FROM-TO display to be changed.  If INSERT/ADVANCE key is pressed, computer will use navigation leg defined by new number in all navigation compu- tations.  If INSERT/ADVANCE key is not pressed, computer will continue using original numbers in all navigation computations; but distance/time information, based on new leg, may be called up and read in data displays (in case of waypoints).  When not in TACAN mix mode, TACAN sta- tion number is inserted to dis- play DIS/TIME information. AUTO-MAN This is a dual purpose control. TEST switch When  the knob is pressed in- ward, the TEST switch function is engaged.  When the knob is ro- tated to either the AUTO or as a selector between those modes. (AUTO) Selects automatic leg switching mode.  Computer switches from one leg to the next whenever waypoint in "TO" side of the FROM-TO display is reached. (MAN) Selects manual leg  switching mode.  Pilot must    make waypoint changes manually. (TEST) When pressed, performs test of INS lamps and displays, remote lamps and indicators controlled by INS, and computer input/ output operations. Used   with   other   controls   to   activate   display   of numerical   codes   denoting   specific   malfunctions   and resets malfunction warning circuits. During alignment, activates the HSI test.  Continued pressing   of   switch   provides   constant   INS   outputs   to drive cockpit displays in a predetermined fashion. NOTE The   INS   can   provide   test   signals   to   the Horizontal Situation Indicator (HSI)and connected  displays.    Pressing  TEST  switch during  Standby,  Align,  or  NAV  modes  will cause all digits on connected digital displays to indicate "8's" and illuminates the HSI  and  ALERT  lamps.    Additional  HSI  test signals  are  provided  when  INS  is  in  Align and the data selector is at any position other than  DSRTK/STS.    Under  those  conditions, pressing   TEST   switch   causes   the   HSI   to indicate heading, drift angle, and track angle error  all  at  "0°"  or  "30°".    At  the  same  time, cross  track  deviation  is  indicated  at  "3.75" nautical miles (one dot) right or left and INS- controlled HSI flags are retracted from view. Output test signal are also supplied to the autopilot when  INS  steering  is  selected.    Rotating  AUTO/MAN switch    to    AUTO    and    pressing    TEST    during    Align furnishes a 15°  left bank steering command.  A 15°  right bank steering command is furnished when the AUTO/MAN switch is set to MAN. FROM-TO Display    numbers    defining display waypoints of navigation leg be- ing flown or in the case of a flashing display, displays TA- CAN station being used. Waypoint numbers automatically change each time a waypoint is reached.  Unless flight plan changes during flight, the automatic leg switching se- quence will always be 1 2, 2 3, 3 4....8 9, 9 1, 1 2, etc. Data selector Selects data to be displayed in data displays or entered into INS.  The rotary selector has 10 positions.  Five positions (L/L 3-45