Speech 讠 brought into harmony all around 周. Read tiáo, it's the act: adjust, mix, tune. Read diào, it's the result: the tone, the tune, the key.
For learners this IS the character of 声调 — the four tones. 空调 air conditioner ('air adjuster') cools every Chinese summer; 调查 diào-investigation fills every news report.
SPEECH tuned all AROUND — ADJUST it (tiáo) until you find the TONE (diào).
空调 'air-adjust' is one of modern Chinese's most elegant coinages — the machine literally named for what it does to the room.