Why zero is marked at south end on a graduated circle of prismatic compass?

Why zero is marked at south end on a graduated circle of prismatic compass?
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Answer :

As bearing of any line is measured with respective north direction, while observing north direction, reading should be 00 0’. Therefore when object vane is bisecting north direction, at the same time zero marked at south end gets reflected through prism. Thus to get bearings with respective north direction always, zero is marked at south end of magnetic needle.
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Related questions

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