Furuno FM-2710 Operator's Manual page 22

9) [DW] Key (Dual Watch mode)
Selects the Dual Watch mode. "DW", "16" and the selected working channel
DW
appear. The radio automatically monitors CH16 (priority), the selected work-
ing channel, and the Weather channel. To return to the receiving mode, press
any key except [INT] and [1/25]/DIM, or turn the Channel selector.
10) [PTT] Switch (Push-To-Talk)
Press to transmit; release to listen. "TX" appears.
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