Internal, 50/200Khz (Dual Frequency), 80/200Khz (Dual Beam), 0
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                   Chartplotter 431s with Dual-beam Transducer
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                   5" GPSMAP� 541s Chartplotter/Sounder with No Transducer
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                   GPSMAP� 441s Chartplotter/Sounder with No Transducer
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                   GPSMAP 421s Chartplotter/Sounder with No Transducer
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                   GPSMAP 521s Chartplotter with No Transducer
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                   GPSMAP Chartplotter / Sounder 531s with Dual-beam Tranducer, 5"
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                   GPSMAP 521s Chartplotter with Dual-frequency Transducer