The article does say "precisely 21cm" in the subtitle, repeats it in the "key takeaways" section, and then close to the end of the article these's this:
>By measuring light of precisely the needed wavelength — peaking at precisely 21.106114053 centimeters
Which I assume is the actual measurement every time "21cm" is brought up in this article.
>By measuring light of precisely the needed wavelength — peaking at precisely 21.106114053 centimeters
Which I assume is the actual measurement every time "21cm" is brought up in this article.