The Si Range is actually the slant range from the transducer. Think back to your geometry days (or daze for some of us! )… remember this:

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Well the Si Range is that side “c”.
Point “B” would be the transducer mounted to the boat.
Side “a” would be the water column (water depth).
Side “b” would be the lake bottom that is shown.


I watched the video that was posted and did not hear Doug contradict this. If I missed something in it, please post back the time stamp for that section.