When configuring a marine echo sounder (ecosonda), what is the vital operational difference between setting the display to 'Depth Below Transducer' versus 'Depth Below Keel'?

1. Depth Below Transducer measures water from the hull-mounted sensor downward, whereas Depth Below Keel offsets for the vessel's draft to show true remaining clearance beneath the lowest point of the keel
2. Depth Below Transducer includes the height of the mast while Depth Below Keel includes tide height
3. Depth Below Transducer works only in freshwater while Depth Below Keel works only in seawater
4. Depth Below Transducer displays radar range while Depth Below Keel displays GPS speed