TM 55-1510-222-10 7.    To  monitor  station  selection  Observe TO-FROM data display. Observe   only   the   number   of   stations   eligible   for mixing will be displayed.  A 0 indicates that none of the 9 stations are eligible for selection. 8.  Monitor INS UPDATE annunciator. NOTE Mixing will not be annunciated if:  (a) TACAN control is inappropriately set; (b)   TACAN   station   data   loaded   in error;  (c)  aircraft  look-down  angle  is greater than 30°; (d) horizontal ground    distance    is    less    than    two times  the  altitude.    When  2  minutes elapse without an update, the NO INS UPDATE annunciator will illuminate. 9.    To  return  INS  display  to  normal  Set data  selector  to  any  position  except WYPT or DIS/TIME. 10.  To monitor program of mix Set data selector   to   DSRTK/STS.      (Observe Accuracy  Index  (A1)  will  decrement to 0.) NOTE To  ensure  favorable  geometry  during the    update    process,    the    following TACAN    station    criteria    should    be observed: · One station must be at least 15 nm off course. · For optimum single TACAN updating,  update  should  continue until aircraft has passed the station.For  optimum  dual  TACAN updating, use one off-track TACAN  station  and  one  on-track station. · For optimum multiple TACAN station updating, the stations should   be   evenly   distributed   in azimuth around the aircraft. 11.  Waypoint thumbwheel Set to number of first TACAN station to be used. Observe selected station number is displayed on the TO side of TO-FROM data display. (10)   Switching   from   aided   to   unaided   inertial operation. 1.  Data selector - DSRTK/STS. 2.  Key 5 - Press. Observe  INSERT/ADVANCE  pushbutton  annunciator illuminates; 000005 appears in right data display. 3.  INSERT/ADVANCE  pushbutton Press. Observe INSERT/ADV'ANCE pushbutton annunciator extinguishes.    Data  display  returns  to  normal  with  5 appearing in first digit of right display. NOTE Benefits    of    previous    aiding    are maintained but no additional automatic updates will be made. (11) To obtain readouts from INS: NOTE The computer is assumed to be in the NAV mode for all data displays. (a) System status:  Data selector DSRTK/STS. Observe  numbers  indicating  system  status  appear  in right data display. (b)  Geographic  present  position:    Data  selector  - L/L POS. Observe   latitude   and   longitude   of   present   position appear   in   left   and   right   data   displays,   respectively. Both displays are to tenth of a minute. (c)  UTM  position:    Data  selector  UTM  POS.Observe northing   and   zone   with   easting   of   present   position appear  in  left  and  right  displays,  respectively.    Both displays are in kilometers. (d)    True    heading    and    MAG    heading:        Data selector - HDG/DA. Observe   aircraft   true   heading   appears   in   left   data display  to  nearest  tenth  of  a  degree.    Press  and  hold keys 3 and 9 simultaneously.  MAG heading appears in left data display to nearest tenth of a degree.  Release keys 3 and 9.  Left display reverts to true heading. (e) Groundspeed: Data selector - TK/GS. Observe groundspeed appears in right data display to nearest knot. (f) Ground track angle:  Data selector TK/GS. Observe ground track angle appears in left data 3-56