Angle measuring device

A device for measuring or marking out angles comprising two discs, each having curved margins extending for most of the periphery thereof, each disc having a slit extending from its center to its periphery along a path defining with a radius a tongue portion, said discs being superimposed so that the tonque portions face and overlie each other, limiting means fixed to each disc at a location radially beyond the curved margin therein and extending in overlying relationship to the other disc and means passing through said limiting means and said discs to mount said discs for relative rotation about a common axis from a closed position in which all but the tongue of each disc lies on one side of the other disc to a position in which further rotation is prevented by said limiting means, the margin of the surface of a disc which faces the surface of the other disc having a scale thereon so that as the discs are moved from the closed position the scale is progressively revealed.