Ruler device for use in marking-off

A ruler device for use in marking-off a workpiece comprising:

• (a) a reference rail which is a straight iron bar having a rectangular cross section and a top surface relieved to form a concave groove;
• (b) a coupling device mounted upon said reference rail, comprising a body having a top portion, a middle portion and a base portion, said base portion bearing rollers located so as to contact the top surface and both side surfaces of said reference rail;
• (c) support rails inserted into the top portion of said coupling device orthogonal to the reference rail, and parallel to each other;
• (d) a scale bar, inserted into the top portion of said coupling device and parallel to said rails, being of rectangular cross section and bearing a concave groove upon its upper surface;
• (e) a support member attached at or near one of its end to the ends of the support rails and scale bar opposite said coupling device, lying in the same plane as said coupling device, having at an end opposite to the attachment to said support rails one or more rollers and being of a length such that, when the reference rail rests upon a plane surface, the support rails will be held parallel to said plane surface;
• (f) a shifting table slidably mounted upon said support rails, having a tool mount essentially in the center and bearing a device for moving said table in the plane of said support rails;
• (g) magnetic tapes fitted into the grooves in the top portions of said reference rail and said scale bar, said magnetic tapes bearing identifiable markings at regular intervals across their lengths;
• (h) identifying devices mounted upon the base portion of said coupling device and upon said shifting table, said identifying devices being suitable to determine the location of said coupling device and said shifting table relative to said magnetic tape portions;
• and
• (i) magnets which attach to said reference rail and hold said reference rail firmly to a ferrous metal surface.