Interesting...I should look at that more. When I flew in the 70'-80's, we were negative dec. around here. We're now positive by almost 11 degs in that time.
I don't bother with declination unless I'm out in featureless territory (ocean/big lake, deep woods) and neither of my favorite compasses are adjustable for declination. In fact, one has no markings at all except a N/S line. ;-)
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paul, texas KD5IVP