There is no standard. If you're using it to keep chair-backs from
banging up your walls, it should be wherever the backs of the chairs
hit the walls. If you're using it decoratively, it should be 38.2%
of the way up the wall, and if anyone asks why, it's because
Y/X=X/(X+Y). If you're a cheap bastard, either the space above
or the space below the rail should be exactly 48", so that
you can use uncut sheet-goods over it, or under it, with no waste.
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