As every parallel of latitude is a circle of 360° the distance from A to B will be the same number of degrees, minutes and seconds whether measured upon parallel AA' or EE', but it will not be the same number of miles as the meridians of longitude are gradually converging toward the poles. On the other hand, the distances from A to C, C to D, D to E, etc., must be the same because the lines AA', CC', DD', EE' are all parallel. That is why the distance is always measured on the latitude scale (i.e. on the vertical border of the chart), and a minute of latitude is always a mile on the chart, no matter in what locality your ship happens to be.
You should be able to understand any kind of information given you on a chart. For instance, what are the various kinds of buoys and how are they marked?
Put in your Note-Book:
1. In coming from seaward, red buoys mark the starboard side of the channel, and black buoys the port side.
2. Dangers and obstructions which may be passed on either hand are marked by buoys with red and black horizontal stripes.
3. Buoys indicating the fairway are marked with black and white vertical stripes and should be passed close to.
4. Sunken wrecks are marked by red and black striped buoys described in No. 2. In foreign countries green buoys are frequently used to mark sunken wrecks.
5. Quarantine buoys are yellow.
6. As white buoys have no especial significance, they are frequently used for special purposes not connected with Navigation.
7. Starboard and port buoys are numbered from the seaward end of the channel, the black bearing the odd and red bearing the even numbers.