A slide ruler is provided to determine how draft copy should be marked in order that the draft might be recopied with spaces added or taken away as needed in order that each line in the final copy will end at a predetermined point to provide an even right hand border. In the ruler, the slide base carries a first scale with fixed left hand index and the slide carries a second set back scale with a fixed left hand index, and a movable right hand index is provided so that a part of the final copy line can be measured between the fixed indices and the remainder of the final copy line can be measured between the fixed index on the slide and the movable index.
A displacement detector which supports either the main scale or the grid to move in a direction perpendicularly intersecting the relative movement direction of the spindle, and which has a spring for pushing one of the main scale and grid toward the other, protrusions for maintaining a predetermined clearance between the urged one of the main scale and grid and the other, and a clearance limiting device for limiting a displacement of the urged one of the main scale and grid from the other to a limited clearance distance to prevent a loss of measuring continuity.
