below zero
零 · 13 strokes
Phonosemantic compound. 雨 represents the meaning and 令 represents the sound. Based on the original meaning "to fall (of rain/snow)". The meaning later shifted to "scattered", "fraction", and "zero".
下 · 3 strokes
Originally a small line or dot below a longer line, indicating "down". The vertical line was added to distinguish the character from 二 (two). Opposite of 上.