Historical clue formulations

• Atomic clock timekeeper — 2021-02-27
• Atomic clock timekeeper — 2019-05-26
• Electromagnetic device — 2013-09-22
• Electromagnetic wave enhancer — 2008-11-29
• Electromagnetic wave amplifier — 2001-05-25
• Part of an atomic clock — 1998-06-24
• Atomic clock device — 1996-08-02