Historical clue formulations

• Tweak — 2017-03-18
• Hone — 2015-04-26
• Make purr, as an engine — 2010-10-29
• Tweak — 2005-09-24
• Tweak — 2004-05-07
• Make just right — 2004-02-13
• Make just right — 2003-11-30
• Tweak — 2002-10-08
• Tweak — 2002-01-12
• Adjust — 2000-07-01