| 摘要 |
PROBLEM TO BE SOLVED: To easily find a one's own staying position and a one's own ship position. SOLUTION: The center of a protractor joined on a triangular rule l by the centering axis 3 becoming a space in the center exists in the center of graduations 4 for determining the length (a nautical mile) of the triangular rule, and exists in the center of an angle adjusting line 5 for understanding a 90-degree part. After adjusting a graduation line of the triangular rule to a target and a target of a transit, 0 degree and 90 degrees of the protractor is adjusted to latitude N and longitude E or a deviation correcting graduation line of a chart.
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