Historical clue formulations

• 1/20 tons: Abbr. — 2013-10-11
• Shipping units: Abbr. — 2011-04-08
• 100-lb. units — 2010-09-29
• 100-lb. units — 2009-07-16
• 100-lb. units — 2008-07-12
• 100-lb. units — 2006-10-18
• 100-lb. units — 2004-11-12