Historical clue formulations

• Letter before zeta — 2025-10-26
• Start of Euripides' signature — 2019-02-10
• Elasticity symbol, in economics — 2014-09-18
• Fifth star in a constellation — 2012-11-16
• Symbol of electromotive force — 2010-05-28
• Fraternity letter — 2009-02-05
• Electromotive force symbol — 2008-11-21
• Delta follower — 2007-05-23
• Small quantity symbol, in math — 1997-03-06