Public domain
Man with a group of 100 kHz quartz crystal oscillators which served as the U.S. National primary frequency standard in 1929
From the collection of Library of Congress. Free to download, adapt and use — no permission needed.
Subjects
Credit lineMan with a group of 100 kHz quartz crystal oscillators which served as the U.S. National primary frequency standard in 1929. 1930-01-01. Harris & Ewing. Harris & Ewing Collection, Library of Congress. Public domain.
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