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Mark Birkle: Libella - Finding the Centerpoint on a Rod
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Mark Birkle: Libella is Not Level
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Mark Birkle: Libella Is Level
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Mark Birkle: Libella Side
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Mark Birkle: Libella Back
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Mark Birkle: Libella Front
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Mark Birkle: Medieval Plumb Bob
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Mark Birkle: Medieval Plumb Bob