| 摘要 |
The navigation aid (1) comprises two transparent discs (2, 3) rotatably secured on top of one another via a central axle (4), the bottom disc (2) being provided with scale markings (5) for angle (6), distance (7) and time (8), and the top disc (3) comprising a reading disc (11) with a rule (12) for reading off the scale markings and speed (9). Each disc has a protruding arm (16, 17) with a point (18, 19), with a line or edge (22, 23) extending between the tip (20, 21) of the point and the central axle. - Distance is measured in minutes or kilometres so that journey time and boat speed can be calculated. |
