Several parts combine into one character.

正 joins 一 on top (a goal line, a city wall) with 止 below (a foot) — the picture of walking straight toward a target. From that came "correct, straight, upright, just." It originally meant "to march straight at a walled town," and the war-sense split off into 征 (zhēng, to campaign).

Mandarin: zhèng, 4th tone is the main reading (correct). Only 正月 (zhēngyuè, the first lunar month) takes 1st tone zhēng — the textbook case of one character, two sounds. 正确 (zhèngquè, correct), 正在 (zhèngzài, in the middle of doing), 真正 (zhēnzhèng, genuine).

Japanese: on-readings セイ (sei) and ショウ (shō), kun ただ.しい (tadashii, correct). 正解 (seikai, correct answer), 正直 (shōjiki, honest), 正月 (shōgatsu, New Year). Japanese also reads 正月 with ショウ, preserving the same special reading as Chinese.

Korean hanja-sound "jeong": 正直 (jeongjik, honest), 正確 (jeonghwak, accurate), 正義 (jeongui, justice). 政 (govern — 正 + 攴, "to set right by force") also grew from this character.

The shared East Asian custom of tallying counts by drawing the five strokes of 正 — one complete 正 = five — comes from this very character (the equivalent of the Western five-bar gate).

Memory aid: a foot (止) heading straight for a line (一) — to go straight toward the goal is to be "correct."