指 zhǐ is pronounced jer in the third tone because zh sounds like the letter j.
指 means to point or to direct.
南 nάn means south and is pronounced in the second tone.
针 zhēn means needle and is pronounced in the first tone.
means south-pointing-needle or compass. In Chinese maps, South is at the top of the page and North is at the bottom. The needle points south in Chinese compasses, not north.
Zhǐnánzhēn zhǐxiàng běibian.
The compass points north.