TM 1-1520-218-10 3C-194 1.  Failure Warning Flag 2.  Altitude Alert Annunciator 3.  Altitude Scale 4.  Barometric     Pressure     Counter     Drum Indicator Window (inches of Mercury) 5.  Barometric     Pressure     Counter     Drum Indicator Window (Millibars) 6.  Manual    Barometric    Pressure    Setting Knob 7.  Altitude Indicator Needle 8.  Counter Drum Altitude Display Figure 3C-143.  Pilots Altimeter (BA-141) In  the  event  of  a  total  ac  and  dc  electrical power loss, the warning flag will be in view, the   altimeter   will   be   inoperative,   and   the indicated altitude will remain as existed at the time of failure. (2)   Altitude  Alert  Annunciator.     The altitude alert    annunciator    illuminates    to    provide    a    visual indication that the aircraft is within 1000 feet of the pre- selected   altitude   during   the   capture   maneuver   and extinguishes when the aircraft is within 250 feet of the pre-selected altitude. After capture, the ALT annunciator  on  upper  right  corner  of  pilot's  altimeter and  ALT ALERT annunciator in the annunciator block above  the  copilot's  airspeed  indicator  will  illuminate  if the   aircraft   departs   more   than   250   feet   from   the selected  altitude,  and  will  extinguish  when  the  aircraft has  departed  more  than  1000  feet  from   the selected altitude. (3)   Altitude Scale.    The  face  of  the  altimeter has a marked scale from 0 to 9 in 20-foot increments. (4)   Barometric Pressure Counter Drum Indicator  Window  (Inches  of  Mercury).    This window indicates    barometric    pressure    as    set    by    manual barometric pressure setting knob. (5)   Barometric Pressure Counter-Drum Indicator     Windows     (Millibars).      The     barometric pressure and millibar counter-drum indicator windows, display barometric pressure in millibars. (6)   Manual Barometric Pressure Setting Knob.   The manual barometric pressure setting knob, placarded    BARO,    is    used    to    set    the    barometric pressure and millibar counter-drum indicators. (7)   Altitude   Indicator   Needle.      The   altitude indicator  needle  points  to  the  altitude  on  the  pointer display between 1000-foot levels in 20-foot increments. (8)   Counter-Drum    Altitude    Display.         The counter drum displays altitude and is marked in 20-foot increments. Altitudes below 10,000 feet are annunciated  by  a  black  and  white  crosshatch  on  the left-hand digit position of the counter display. c.   Operating Procedure. NOTE If the altimeter does not read within 70 feet of   field   elevation   when   the   correct   local barometric   setting   is   used,   the   altimeter needs   calibration   or   internal   failure   has occurred.  An error of greater than 70 feet also  nullifies  use  of  the  altimeter  for  IFR Flight. 1.   BARO     knob     –     Set     desired     altimeter setting. 2.   Warning flag – Check not visible. 3.   Needle indicator  – Check operation. WARNING