I suppose I could have got synchronised time data from the clock to a computer if I'd pointed a webcam at it, but I'm not sure I'd have considered the result reliable enough to call stratum 0.

Still rather closer to stratum 0 than my hack which used a TV card to scrape the TeleText clock... (Back in the days of dial-up, when any non-Internet clock source at all started to seem like a good idea.)

On a related note, I'm constantly amazed that mobile phones do not appear to grab accurate time from their networks. Surely the network itself maintains an accurate clock, so why the heck does anyone ever have to set a phone's clock (innacurately) by hand?

My last phone did get the time from its network, but – perhaps even more inexplicably – it was configured not to do so by default. No idea why.

IIRC a friend of mine who configured their phone to use network time found that it was several minutes slow...