| 摘要 |
<p>The present invention relates to parallel rulers for use in navigation. The ruler comprises at least three elongate members (2 to 4) each linked to an adjacent one of these members by a pair of arms (5, 6) of equal length. The arms (5,6) are pivotally mounted at each end to said adjacent members such that for each pair of arms, the pivot points of a pair of arms on any one member define, with those on an adjacent member, the corners of a parallelogram.</p> |
