Two curves which, at any point, have a common principal normal vector are called Bertrand curves. The product of the torsions of Bertrand curves is a constant.

# Bertrand Curves

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## Cite this as:

Weisstein, Eric W. "Bertrand Curves."
From *MathWorld*--A Wolfram Web Resource. https://mathworld.wolfram.com/BertrandCurves.html