it the angle of the dangle, so to speak! \:D I have a speedo on my boat, one on my fish finder and one on the gps (when my buddy lets me borrow his) and never look at them when trolling. I watch the cable angle and vary speed so it stay about 40 degrees or so for silvers.
as for frozen herring I only use it for teasers on my hootchies. I like fresh if I am going to plug cut them. I do let them thaw, but don't let them get warm. A brine can help make them a little tougher.
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bawddawg, no biscuit!