String surface model, hyperbolic paraboloid; a skew quadrilateral with its opposite sides equal in length and pierced with holes at equal distances

Hyperbolic paraboloid, a skew quadrilateral with its opposite sides equal and strings equally spaced.This is one of a large set of ruled surface models made by Fabre de Lagrange in Paris, France, following designs introduced in the early 19th century. They illustrate surfaces which can be traced out in space by the movement of a straight line. This model consists of a series of threads strung across a skew quadrilateral with its opposite sides equal in length.