Regŭla
（κανών). A ruler for drawing straight lines on plane surfaces; as the perpendiculum (στάθμη） was used for a vertical direction (Vitruv. vii. 3, 5). The name regula is also applied to the thread of the screw (Blümner, Technologie, iv. 124).
Harry Thurston Peck. Harpers Dictionary of Classical Antiquities. New York. Harper and Brothers. 1898.
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