Combination drafting instrument

Claim 1

A drafting instrument comprising: a thin, flat, circular, transparent disc having a peripheral edge, the periphery of said disc being subdivided into degrees by radial degree marking lines throughout 360*, at least some of said degree marking lines at regular intervals including pencil-receiving guide holes extending through said disc inwardly of said peripheral edge, at least some of said degree marking lines including progressive degree indicia, said disc having a center through guide hole, said disc being subdivided into 90* segments by a first set of straight radial rows of through guide holes extending outwardly from said center guide hole to a peripheral portion of said disc at intervals along a pair of primary diameters of said disc to subdivide said diameters into lineal units of measure, said first pair of diameters including lineal dimension marking lines therealong perpendicular to said diameters and subdividing said diameters into lineal units of measure, at least some of said guide holes of said primary diameters extending through said lineal dimension marking lines, at least some of said dimension marking lines along both of said first pair of diameters being identified by progressive lineal dimension indicia comprising numbers increasing progressively in value radially outwardly from said center guide hole in opposite directions along said primary diameters so that said center hole provides a zero reference point, said disc being subdivided into 45* segments by a second set of straight radial rows of through guide holes extending outwardly from said center guide hole to a peripheral portion of said disc at intervals along a pair of secondary diameters spaced at 45* from said primary diameters, to subdivide said seconday diameters into lineal units of measure, and a plurality of pairs of sight guide lines extending from guide holes of said secondary diameters toward said primary diameters with each guide line of each pair being perpendicular to the other guide line of said pair and perpendicular to the primary diameter toward which it extends and with said sight guide lines being aligned with said lineal dimension marking lines of said primary diameters, said pairs of sight guide lines of one said secondary diameter being aligned with said pairs of sight guide lines of the other said secondary diameter so that said pairs of sight guide lines collectively define a series of concentric squares symmetrical about said center guide hole.