TM  1-1520-240-10            2-14-7 2-14-21.  CHRONOMETER. Two digital clocks labeled CHRONOMETER are located on the copilot and pilot instrument panels (fig. 2-14-4). Each clock has a six-digit GMT (greenwich mean time) display and four-digit selectable display. A test mode is provided to check system. A flashing annunciator identi- fies  which  clock  mode  has  been  selected.  There  are three controls on each clock, a SELECT button, a CON- TROL button, and a DIM switch. Figure  2-14-4.  Chronometer a. SELECT Button.  It allows the selection of any of three  modes  on  the  four-digit  display:  GMT,  LT  (local time), or ET (elapsed time). The six-digit display shows GMT only. b. CONTROL Button.  It is used to set the time se- lected on the four-digit display. When the CONTROL and SELECT buttons are pressed simultaneously, the four- digit display is changed from the normal to the time set mode, and the CONTROL button is functional. c. DIM  Control  Switch.  It  is  used  to  set  the  light intensity of the display. At low light settings, the clock display is NVG compatible. Integral alkaline batteries maintain clock operation when no aircraft power is applied, but the CONTROL and SE- LECT buttons are disabled. Power to operate the chro- nometers is supplied by the DC essential bus through the CPLT CLOCK and PLT CLOCK on the No. 1 PDP and No. 2 PDP. 2-14-22.  Normal Operation - CHRONOMETER. 2-14-23.  Setting GMT. Press the SELECT button until GMT is selected. Simulta- neously press both the SELECT and CONTROL buttons to enter the set mode. The tens of hours digit will start flashing and the CONTROL button has full control of the flashing digit. Each time the CONTROL button is pressed , the flashing digit will increment. Once the tenth of hours is set, pressing the SELECT button will select the next digit to be set. After the last digit has been selected and set with the CONTROL button, press the SELECT button to  exit  the  set  mode.  The  annunciator  will  resume  its normal flashing condition to indicate that the GMT clock is running. 2-14-24.  Setting LT. Press the SELECT button until LT is selected. Simulta- neously press both the SELECT and CONTROL buttons to enter the set mode. The tens of hours digit will start flashing  and  CONTROL  button  has  full  control  of  the flashing digit. Use the same sequence as for setting GMT with the exception that the minutes are already synchro- nized with the GMT clock and can not be set when in LT mode. 2-14-25.  Setting ET. The  elapsed  time  allows  for  count  up  or  count  down modes. a. Count Up.  Press the SELECT button until ET is selected. Press the CONTROL button to start count up sequence.  The  clock  will  count  up  to  59  minutes,  59 seconds and then changes to hours and minutes. It will count up to 99 hours and 59 minutes. Pressing the CON- TROL button again resets the ET to zero. b. Count Down.  Press the SELECT button until ET is  selected.  Simultaneously  press  both  SELECT  and CONTROL buttons to enter the set mode. A count down from any time, not to exceed 59 minutes and 59 seconds, can be set using the same sequence as for setting GMT. Once the last digit is set, pressing the SELECT button exits the set mode and the clock is ready to start count down.  Pressing  the  CONTROL  button  will  start  count down sequence. When the clock reaches zero, an alarm becomes  active  by  flashing  the  numbers  and  the  ET counter will begin to count up. To reset the alarm press either the SELECT or CONTROL button. 2-14-26.  Test Mode. To activate the test mode, press and hold the SELECT button for three seconds and all numerical displays will show an 8 and all annunciators will be active. 2-14-27.  Master Caution System. The  master  caution  system  provides  the  pilots  with  a visual  indication  of  helicopter  conditions  or  faults  (fig. 2-14-5 and 2-14-6). The components of the systems are the   712  Master Caution Panel with NVG filter,   714A Master  Caution/Advisory  Panel,  two  MASTER  CAU- TION lights with NVG filters, and a CAUTION LT panel with a TEST and BRT-DIM switch. Power to operate and control the master caution system is supplied by the DC essential bus through the LIGHTING CAUTION PN cir- cuit breaker on the No. 1 PDP.