12,966. Porter, A. Bowmar-. June 4. Mathematical drawing-appliances. -A device for enabling students to determine the dimensions of an object as seen in perspective consists of a rectangular frame A having graduated edges adapted to receive two graduated bars C, D which may be moved to bound an aperture through which the object is visible. The bars may be moved by the fingers or by screws, and may be fixed in their adjusted positions by screws.
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