| 摘要 |
A compass, comprising a sliding rod with a handle at an upper end, and a drawing portion. A slider is slidably mounted on the sliding rod. Two links are pivotally connected to the slider and to the drawing portion at respective first pivot points forming at least approximately a parallelogram. A crank is operatively pivotally connected to the sliding rod and to a center of one of the links at respective pivot points, the crank having a length between its pivot points equal to half the length of the link to which the crank is connected between the first pivot points of the one link.
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