Protractor with a rotor

A protractor comprising:

• a main body surrounding a circular aperture, said main body having a scale of angular measurements thereon, and said main body having an upper main face and a lower main face;
• and
• a rotary cursor mounted on said main body for rotary movement about the centre of the circle of the circular aperture, said rotary cursor comprising a part-circular centre portion engaged in said circular aperture and rotatable within said aperture, and an arm portion extending radially outwardly from said centre portion to said scale;
• said arm portion having a reference feature which can be aligned with selected positions on the angular scale of the main body, and said centre portion having an upper main face, and a lower main face, and having a reference side edge and a further side edge, said reference side edge extending along a radius of the circle for alignment with a side of an angle to be measured, or for indicating an angle to be marked, whereby said reference side edge can be aligned to a position related to an angle on the said scale of angular measurements, said reference side edge of said centre portion being formed at the intersection of said lower main face of said centre portion and an inclined bevel face of said centre portion which is inclined to said upper main face of said centre portion, said inclined bevel face bearing a linear measurement scale,
• said centre portion of said rotary cursor being generally in the shape of a sector of a circular disc bounded by said reference side edge and said further side edge, said sector extending through about three quarters of a circle from said reference side edge to said further side edge, said arm portion and said centre portion of said cursor being formed as an integral unit with said reference side edge and said further side edge fixed relative to each other, said centre portion being in engagement with the perimeter of said circular aperture along about three quarters of the perimeter of the circular aperture, and the underside of said centre portion presenting a continuous surface over the lower main face thereof extending around a sector of about three quarters of a circle, for contacting a surface on which the protractor is resting;
• said lower main face of said centre portion lying in the same plane as said lower main face of said main body whereby when a line is drawn along said reference side edge on paper on which the protractor is resting said reference side edge is touching said paper to minimize parallax errors.