Mission and Event Timers
Both the Command Module and Lunar Module have mission and event timers on the control panel. The Mission Timer is used to show the elapsed time since liftoff, whereas the Event Timer can be used for counting up or down to or from mission events.
Mission Timer
The Mission Timer can only count up, not down, from a minimum of 000:00:00 to a maximum of 999:59:59. The Mission Timer is automatically reset to zero at liftoff, and you can use the START/STOP/RESET switch on Panel 2 to start it running, stop it temporarily, or reset it to zero. In general, however, you will start it and leave it running forever after, unless you have a need to update the mission time displayed.
The time displayed can also be updated with the HOURS/MIN/SEC switches. The switches are spring-loaded to the center position, but clicking them down will increase the appropriate value (hours, minutes or seconds) by one, and clicking them up will increase it by ten. You can only increase the time, to reduce it you have to 'go around' back to zero and start again.
The Mission Timer requires both 28VC and 115V AC power, and a 10Hz signal from the central timing equipment in the spacecraft. It can operate by using an internal tuning fork as a reference if the timing signal is lost, in which case a small timing fork symbol will be displayed in addition to the time. Currently this is not implemented in Orbiter.
Event Timer
Unlike the Mission Timer, the Event Timer can count down as well as up.
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