Par′al-lel Rul′er.
A draftsman's instrument, consisting of two wooden or metallic blades, so joined together by jointed cross-pieces as to open to different intervals and yet retain their parallelism. A still simpler form is a rolling cylinder a. b is the ordinary form of two--leafed ruler with two links. c is a two-leafed ruler with cross links. d is a three-leafed ruler, the middle section being united by links to the main sections. e is a flat ruler with a pair of grooved wheels, fixed on an axis, rotating in bearing-posts fastened to the ruler. Fig. 3552 is a form of ruler having a graduated ruling-blade moving in contact with a graduated blade which represents the vertical. In the two parallel arms of the ruler are slots parallel to the edge of the ruler. Through these slots pass pins from the ends of cross-arms, the other extremities of which [1632] are pivoted to the two parts of the ruler; distances apart of the bars are measured on the vertical bar.Parallel rulers. |
Parallel ruler. |