Rul′er.
An instrument with straight sides, for guiding a pen, pencil, or scriber in drawing straight lines.
The fiducial edge, when divided, enables linear measurements to be laid down therefrom.
The
regula (ruler) of the ancient
Romans was thus divided, as are the rules of carpenters and other artisans at present.
Desk-rulers are either flat or round; the first have a beveled edge to prevent ink flowing from the sides of the pen on to the paper.
The round form is very convenient for ruling parallel lines by one accustomed to its use.
The common parallel ruler is composed of two straight-edged arms, which are kept parallel by means of two pieces pivoted to each.
Sometimes an intermediate parallel piece is interposed, or a single straight-edge, having a roller near each end, is employed.
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Rulers. |
The universal adjustable ruler (
a,
Fig. 4497) comprises a graduated straight-edge and a protractor, enabling angular measurements to be made or parallel lines to be drawn at any angle with the edge of the table or drawing-board.
The ruler
b is also adapted for drawing parallel equidistant lines; the protractor being dispensed with.
There are several varieties used for drawing parallel lines.
a. Two-part ruler; the most usual kind.
b.
Dollond's ruler; has a roller near each end.
c. Three-part ruler.
d. Cross-brace ruler.
The draftsman's table is provided with two triangles: one having the angles of 45° and 90°, and the other, 30°, 60°, and 90°. By holding the former of these steady with the left hand, at such an adjustment that the edge of the triangle shall be coincident with the given line, a line parallel with the said line may be obtained either above or below it, by slipping the triangle
b on the triangle
a.
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Parallel rulers. |
e has a metallic straight-edge imbedded in the face.
Other rulers have parallel hinged slats, or consist of an elastic straight-edge, which will yield to the bent pages of a record or account-book; a straight-edge considerably elevated from the paper to prevent ink soiling the latter; one provided with clamps to secure it to the edges of a book; containing recess for holding pencil or pen, made of folded, sheet metal or both: T-shaped for ruling lines parallel or at right angles to edge of book.
