The cardinal point on the mariner's compass90= clockwise from due north and directly opposite west.
东方航海罗盘上一个基本方位, 正北方向顺时钟转90°或指正西的相反方向
The cardinal point on the mariner's compass270= clockwise from due north and directly opposite east.
西航海者指南针上的基本方向, 即从正北按顺时针方向转270度, 正对着东方