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"As the eccentric turns in the strap, the point O moves in the dotted circle around O', and the point A also moves in a circle. When half a revolution is accomplished the point O will be at O", the Point A will be at A", and the eccentric strap and valve rod will be in the position indicated by the dotted lines." —Derr, 1911

Shaft in an Eccentric Motion from Steam Engine

"As the eccentric turns in the strap, the point O moves in the dotted circle around O', and the point…