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Well, I have plenty of those (and often the mag difference or other metallic structures, can easily throw them off in the observatory); just walk around with one.
For this application, aside from owning a compass, is a mobile PierTech trailer observatory. Often, one cannot easily "park" this 9x9 device so that its internal pier is within 5 degrees of the NSP and many times you don't have a choice as to where to back it in a field and park in an assigned star party slot.
Therefore, I need to rotate the mount as much as 270 degrees on occasion before I do my temporary pier modeling.
I agree North is easy to find.....