TM 55-1510-222-10 improper  control  settings.    It  is  also possible  to  get  a  good  Mode  C  test on  the  transponder  control  with  the OFF  flag  showing.    If  the  OFF  flag remains visible, radio contract should be made with a ground radar site    to    determine    if    the    altitude reporting function is operative. b. Pilot's Altimeter - Normal Operation. (1)   Turn-on  procedure:    Servoed  altimeter  will operate  when  avionics  master  switch  is  turned  on  and single phase AC is on. (2) Operating procedure: 1. Barometric    set    knob    -    Set    desired altimeter setting in IN. HG. window. 2. OFF flag - Check not visible. 3. Needle indicator - Check operation. 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. c. Pilot's Altimeter - Emergency Operation. Disregard pilot's altimeter and utilize copilot's altimeter. 3-34. COPILOT'S ENCODING ALTIMETER. a. Description.    The  copilot's  altimeter  (fig.  3-27), provides    an    indication    of    present    aircraft    pressure altitude above sea level.  It also supplies information to the   INS   and   GPS.      The   air   data   computer   supplies altitude information to the transponder. b. Controls/Indicators and Functions. (1)   ALT alert indicator.  Not used. (2)   Altitude   pointer   display.      Displays   aircraft altitude  in  hundreds  of  feet.    Subdivided  into  20-foot intervals. (3)   MILLIBARS window. Indicates local barometric pressure in millibars.  Adjusted by use of set knob. (4)   IN  HG  window.    Indicates  local  barometric pressure  in  inches  of  mercury.    Adjusted  by  use  of  set knob. (5)   BARO     knob.          Used     to     manually     set barometric   pressure   displayed   in   the   MB   an   IN   HG windows. (6)   Test     button.          Used     to     test     altimeter operation. (7)   Drum indicator.  Indicates aircraft altitude in ten-thousands,  thousands,  and  hundreds  of  feet  above sea level. (8)   CODE  OFF  flag.    Indicates  possible  failure of encoder transmission. c. Encoding Altimeter - Normal Operation. (1)   Turn-on  procedure:    Encoding  altimeter  will operate  when  avionics  master  switch  is  turned  on  and single phase AC power is on. (2)   Operating procedure: 1. Barometric    set    knob    -    Set    desired altimeter setting in IN. HG.  window. 2. CODE OFF flag - Check not visible. 3. Needle indicator - Check operation. 4. TEST button - a. Push  -  Reading  decreases  by  500 feet. b. Release    -.        Returns    to    original reading. 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. d. Encoding    Altimeter    -    Emergency    Operation. Altimeter circuit breaker - Pull (if encoder fault occurs). 3-82