this already is a 20yo site or so. why the hype today?

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There's a lot of interesting stuff in the time-nut world. There's a fun mailing list at https://time-nuts.febo.narkive.com/ and Jeff Geerling has been doing a lot of stuff with clocks lately on YouTube. An interesting intro project is to set up a GPSDO and track the long-term aging of an OXCO or Rubidium standard (many of which are surplused out of telecom applications for somewhat reasonable prices on eBay).

Also vaguely related, the precision clock kit by Mitxela - https://mitxela.com/shop/clock4

Then there's the EFOS3 Hydrogen Maser by https://www.efos3.com/

There is a very deep rabbithole in here.