| 摘要 |
In a preferred embodiment, there is provided a combination of a windowed indexed calibrated T-square and a precision-lined drafting board for use therewith for providing scaled drawings on drafting paper transparent to the drafting board's precision lines, the window being positioned in the helve head such that the index line positioned along a lower edge of the window is alignable with and positioned over the drafting board's precision lines when flat roller surfaces of spaced-apart x-axis aligning rollers on the helve head are pressed flushly against upright flat linearly-extending edge of the drafting board with the edge extending along the x-axis of the drafting board, with the roller surfaces being of broad width affording non-wobbling stable positioning of the blade of the T-square relative to an upper face of the drafting board when the T-square has the roller surfaces pressed flushly against the flat surfaces of the upright flat linearly-extending edge of the drafting board.
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