I see that Maretron’s DSM150, DSM200, and DSM250 displays have a DST100 configuration setting called "Transducer Depth Offset:"; what is this?

Transducer offset is either

• the distance from the waterline to the transducer (DST100 bottom surface), or
• the distance from the transducer to the bottom of the vessel.

Maretron display products (DSM150, DSM200, DSM250, and N2KView) add the transducer offset value to the depth reading to produce the desired reading. For example, if you want to know the water depth, you program a positive value into the DST100 for the transducer offset. If you want to know the depth of water underneath your boat, you program a negative value into the DST100 for the transducer offset. To further clarify, if the transducer (DST100) is mounted two feet under the water and the draft of the boat is 5 feet, you would program 2 feet for the transducer offset if you wanted to know the depth of the water or you would program minus three if you were interested in knowing how deep the water was underneath your vessel. Maretron displays automatically add (or subtract) the transducer offset to show you the water depth or depth under the vessel respectively.