Historical clue formulations

• Measure the depth of — 2024-08-01
• Downright — 2023-11-12
• Vertically level — 2023-04-16
• Get to the bottom of — 2019-02-24
• Downright — 2009-02-27
• Perfectly vertical — 2006-06-28
• Perpendicular — 2005-05-17
• Depth checker — 2003-11-30
• Downright — 1999-05-15
• Carpenter's gadget — 1998-06-16