installations,  is  the  OA-7900/GMQ-10  converter/ indicator group. It provides a LED digital display of runway visual range in hundreds of feet. The AN/GMQ-32 system is an upgrade of the AN/GMQ-10  system.  This  major  change  replaced  the vacuum-tube electronics of the AN/GMQ-10 with solid-state  circuitry.  The  external  appearance  of  the equipment  was  not  changed.  The  equipment  still  retains the original identification plates. INDICATOR/RECORDER  UNIT The  ID-353B/GMQ-10(B)  or  the  ID-820/GMQ- 10(C) transmissometer indicator/recorder unit (fig. 2-35) is found in the observer’s work area of Naval Meteorology and Oceanography detachments and Marine  Corps  weather  offices.  The  only  visible difference   between   the   two   models   is   that   the calibration setting meter is found only on the ID-353B, which was originally designed for use overseas where the local electricity did not conform to the carefully maintained 60-hertz AC found in the United States. Operation The  transmissometer  equipment  is  normally  left  on. It is turned off only for maintenance.   If the system has been  turned  off,  start-up  calibration  adjustments  are required after a 1-hour warm-up period. Detailed operational procedures for the upgraded AN/GMQ-32 system, including the ID-353/GMQ-10 and   ID-820/GMQ-10   transmissometer   indicator/ recorder, are found in Air Force Technical Order (AFTO)  31M1-2  GMQ-32-1,  Operation  Manual, Transmissometer  AN/GMQ-32,  provided  with  each equipment   modification. Instructions provided in NAVWEPS 50-30GMQ-10-2,  Technical Manual, Operation  and  Maintenance  Instructions  with Illustrated  Parts  Breakdown,  for  the  mechanical components, such as the spring chart drive, are still valid and may be used if the AFTO is not available. Instructions  and  criteria  for  use  of  transmissometer  data are contained in NAVMETOCCOMINST 3141.2. The  transmissometer  indicator/recorder  provides two  output  readings:  the  recorder  graph  and  the transmissivity   meter.   Both   outputs   provide transmissivity percentages. Two sensitivity settings are used to process incoming data. The indicator/recorder is normally operated in the LOW sensitivity setting, but the HIGH sensitivity setting may be used during low- visibility conditions, when transmissivity falls below 20%.   The   HIGH   setting   simply   multiplies   the indicator/recorder  output  by  5,  which  allows  the operator to read the output more accurately. Both readings  must  be  corrected  for  background  illumination and  converted  by  using  the  tables  provided  in NAVMETOCCOMINST  3141.2  to  yield  runway visual range or sector visibility. The background illumination correction is found by placing the Background switch in the TEST position, obtaining  a  background  illumination  level,  and  then subtracting the background illumination level from the transmissivity  reading  to  obtain  a  corrected transmissivity reading. The   runway   visual   range   (RVR)   table   in NAVMETOCCOMINST  3141.2  is  in  two  sections: one for use during the day and the other for use at night. Columns are provided for runway light settings (LS) 5, 4, 3, and Other. The Other column is used when runway lighting is either not in operation or at setting 1 or 2. The runway light setting is obtained from the air traffic controllers. Use the transmissivity value in the proper light setting column to find RVR. Maintenance General maintenance for the AN/GMQ-32 system is performed by base ground electronics personnel or trained   METEM   (METeorological   Equipment Maintenance)  Electronics  Technicians.  Refer  to  the care-and-use   publications   for   more   detailed information. The following routine maintenance is usually performed by the observer: Replacing the recorder paper—Replace the paper by using the reloading diagram exposed in the recorder  window.  Charts  in  continuous  operation  run  at 3 inches per hour and are normally changed every 2 weeks Rewinding   the   recorder   chart   drive spring—Rewind  when  setting  the  recorder  chart  time  or once per week. A fully wound drive will operate for 8 days Adjusting the recorder zero adjustment—Adjust daily when the recorder is in use Refilling/cleaning  the  inkwell  and  pens—Empty and clean inkwells, indicator pens, and marker pens once a month. In many recorders, the inkwells have been removed and pen cartridges have replaced the ink pens 2-26