Carl crappiepappy has it nailed and spot on with his answer to you.
I'm not sure how you fish but when I first started crappie fishing I was interested is how to set the Depth Offset on my graph and finally realized as for me it really didn't matter that much since my trolling motor depth it is running in the water is continually changing as it always eventually slips deeper into the water over time. When it finally slips to its maximum depth I'll adjust it up shallower since I don't like it running that deep where I can't see the underwater stobs that I'll run into. I think Minnkota sells an additional attachment that will more securely hold the trolling motors depth setting.
Now for some of the reasons I didn't find it necessary to set the Depth Offset. I normally tight line hover with rods in both hands. If I'm working suspended fish where I can see scattered individual fish marks on my graph it tells me at what depth they are running. At what depth they actually are suspended at doesn't really matter because I can also see the depths my baits are running on the graph. I them make sure my baits are running at the same depth I'm seeing my fish marks.
If I've established that there are fish on the bottom to be caught at a given depth it doesn't really matter what the real actual depth is as long as I stay where my graph shows that given depth.
Again if I've established there are catch able fish on a break from say 15 ft into 20 ft as shown on my graph it still doesn't really matter if those actual depths are 12 and 17 or 19 and 24 as long as my graph shows it at 15 to 20ft.
Just my thoughts on this which now definitely confirms my lazy indolent approach towards fishing where I try and catch fish with the very least or minimal amount of input efforts towards actual catching and which those that already know me are well aware of.
“There is no difference between communism and socialism, except in the means of achieving the same ultimate end: communism proposes to enslave men by force, socialism—by vote. It is merely the difference between murder and suicide.” Ayn Rand