| 摘要 |
The instrument is a flat transparent rectangular ruler, 30cm by 7cm. Engraved or printed on the ruler are a number of compass roses and scales. Along the upper and lower edges are nautical mile scales for 250,000:1 (1) and 500,000:1 (2) charts. The left hand rose (3) is a QDR-FROM rose used to determine course and distance from a station to a destination and allowing for drift. The right-hand rose (4) is a QRM-TO rose used in a similar way to the QDR-FROM rose, but to the station rather than from it. The central rose (5) is used for on-route course changes. - The horizontal centre line carries nautical mile scales (6,7) from the two outside rose centres. Drift angle markers (8,9) from the central rose can be used for on-route corrections, and a marker hole (10) is used on route to find true or magnetic north.(/1)
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