Today in History is a daily newsletter from Britannica. (more) Today in History—April 5: The U.S. Joins the Metric System—Sort Of Written by Erik Gregersen Erik Gregersen is a senior editor at Encyclopaedia Britannica, specializing in the physical sciences and technology. Before joining Britannica in 2007, he worked at the University of Chicago Press on the... Erik Gregersen Fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated Apr. 2, 2026 •History Who gets to say how long an inch is anyway? On this day in 1893, physicist Thomas Corwin Mendenhall did. And it has more to do with the metric system than you might expect. Today in History is a daily newsletter from Britannica. Encyclopædia Britannica, Inc. Today in History is a daily newsletter from Britannica. Want to learn more about what happened on April 5, or any other day of the year? Sign up to...

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