These rules are often combined with the mnemonic “West is Best, East is least”; that is to say, add W declinations when going True headings to Magnetic Compass, and subtract E ones.

从真北至磁北，加西磁差，减东磁差。从真北到磁北的过程最常用。因为在判断落地侧风时，报文风向是真北，要换算成磁北才能和跑道比较出夹角。

True to Mag, West is Best.

不押韵，我觉得还是很难记。