| 摘要 |
The support is graduated in length scales (1,2,7,8) on opposing edges with scales (1 and 7) starting from the same corner of the support so the two opposing scales (1,2) address diagonally opposite corners of the rectangular support. The opaque support should be transparent along one scale (3) over part of its width. A central length scale (3) between the two parallel scales (1,2) starts from one of the transverse edges and has a transparent strip (4,6) along its length, the strips in turn divided by an opaque strip (5).
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