# “Cycles” to “Hertz”: Why the shift circa 1970?

Before circa 1970, it was more common to say "kilocycles" than "kilohertz" (and analogously for "mega-," "giga-," etc.). What contributed to "Hertz" becoming more common than "cycles"?

### SI units started to be used.

In 1960 (not 1970!), the Système international d'unités was established at the General Conference on Weights and Measures. The hertz was officially recognized as a unit derived from metric system units (namely, the second). It was already in partial use (the International Electrotechnical Commission began using it in 1930). With the rise of the hertz, the phrase "cycles" in "cycles per second" fell out of fashion, leading to the general trend we see on the Google Ngram.

Interestingly enough, adding "hertz" to the Ngram search shows that its usage, too, took off a bit after 1960, though it was already fairly popular.

• Ah, good distinction: "started to be used". SI units are much older than 1960. – Geremia Jan 7 '17 at 22:31
• If you add "kHz" and "MHz" to your ngram search, you'll see they take off sooner and much, much more dramatically than "kilohertz" and "megahertz". – Russell Borogove Jan 8 '17 at 2:13

There was indeed some resistance to adopting the new name in the United States. In 1967, Rufus Cartwright wrote about it in the magazine Electronic Illustrated":

Is the short, illustrious life of Heinrich Hertz any reason to change the English language? A quick answer is no, especially since hertzian waves and antennas already honor him. But that may be the short view. Perhaps we must take the long view and see life as a complete hertz.

What might have helped in popularizing the new unit is that saying 'cycle' is potentially confusing when 'cycle per second' is really meant.

• An older physicist once told me he had a most FRUSTRATING experience in discussing a phase-locked loop, when he noted that the locked loop was different from the reference by a quarter cycle... and was immediately interrupted by an excited engineer who said the frequencies couldn't be tolerated to be so different. – Whit3rd Jan 18 '17 at 9:51

The General Conference on Weights and Measures (1960) adopted the herz unit. So you have found that it took about 10 years for English-speaking books to catch up with that change.