An adjustable straight edged device for use with a drafting board includes a straight edged blade which is adjustable to different angular orientations on the drafting board and is positively and precisely aligned in a horizontal orientation across the board. The device includes a platform slidably mounted for movement along one side of the drafting board on which the blade is mounted. The platform includes a pivot pin and preferably guide pins which are disposed to respectively, engage an elongated slot and pins about an end angle provided on the straight edged blade to slidably and pivotally attach the blade to the platform. In an alternative embodiment a single guide pin is used which engages a notch in the straight edged blade. This arrangement allows the straight edged blade to be repeatedly and accurately aligned in its horizontal orientation. A clamping knob is provided on the pivot pin for locking the blade in place on the platform. The device also includes a right angle attachment and a sliding scale adapted for sliding movement along the straight edged blade.
