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For the simplified wall perimeter which I present I claim nothing original except the idea for the wall suspension.
The wall clamp was taken from an old gynecology table. The supporting bar was made by a blacksmith. Both pieces were chrome plated. The perimeter arm is ¾ inch (1.9 cm.) plywood and is graduated to measure 100 degrees. It was given four coats of jet black paint. I had previously put on four coats of a neutral gray but found that the black paint is much more satisfactory. The point on the end of the arm was a brass cup hook which was straightened out and filed to a point. It points directly on the protractor to the meridian which is being examined. A wooden drawer knob has been screwed onto the back of the arm in order that one may hold it in position by hand in the oblique
AMBROSE A. A SIMPLIFIED PERIMETER OF WALL TYPE. Arch Ophthalmol. 1949;41(5):633-636. doi:10.1001/archopht.1949.00900040649013