The book Longitude by Dava Sobel tells the story of John Harrison who figured out how to calculate how far east or west a ship was on the ocean.

达瓦索贝尔写的这本书《经度》讲述了约翰哈里森如何计算出轮船在海面上从东到西航行距离的故事。

youdao

But they believed the magnetism to be of little use in judging longitude, leaving it a mystery as to how the turtles know their east from west.

然而，他们认为在辨识经度上磁场帮不上忙，所以海龟如何分辨东西方位仍然是个谜。

youdao

These squares are identified by two-letter digraphs: the first letter is the east-west position within the longitude zone and the second letter is the north-south position.

这些方块使用两个相连的字母标识：第一个字母表示经度区的东西位置，而第二个字母表示南北位置。

youdao

So each hour's time difference between the ship and the starting point marks a ship's progress of fifteen degrees of longitude to the east or west.

VOA: special.2010.07.14

For a mission, the pair move south to the equator at 154 degrees West Longitude.

BBC: Science & Environment

For a mission, the rig and control vessel are moved south to the equator at 154 degrees West Longitude.

BBC: Sea Launch rocket company returns to service

They achieved one of the most hotly contested aviation goals on Saturday when they passed over Mauritania and crossed the 9 degrees west longitude mark -- the official finish line for their flight around the world.

CNN: Balloonists: '20 days of beautiful moments'