We have several VCRs and a few other devices that automatically get the correct time and automatically adjust for GMT/BST.

I've always thought they got the time from the TV signal through the ariel however a friend seems to think they get the correct time from the mains power. I've never even heard of the mains carrying the current time so is he correct or am I correct in thinking they get the time from the TV signal?

Yes they do.

lol, getting it through the mains power!

would be good if it did actually. you wouldnt have to set the time on your microwave, oven, bedside clock, etc.

You can get such devices that will set their own time. They don't do it via the mains though it's still radio.

Actually getting the time through the mains isn't a ridiculous idea though I don't think it's done anywhere - largely because there's no profit in it. However using the power lines for meter reading (much more difficult than clock setting) is done.

i have got a little alarm clock that sets its time through the radio waves (well its supposed to - but doesnt half the time )

I didn't know they use it to read electricity meters.

I wish someone would tell the guy who keeps waking me up by banging on my door, wanting to be let into the garage to read the bloody meter!

My friend has told me why he thought VCRs took the time from the mains. His Hard Drive recorder hasn't got any ariel plugged into it, only his Sky box through Scart and when he selected 'Auto-Time' on the recorder, it automatically got the correct time.

How is that possible without an ariel connected? Or can it get the time through the Sky Digibox?

i didnt think the scart could pass the time through it?

mind you, saying that... you did used to be able to get analogue teletext through sky digital channels, so I guess it would be possible?

Will the time be more accurate through a Russ Andrews mains lead?

Unfortunately although the technology exists and is used in some places around the world it all depends on costs. At the moment the meter owners mostly think it's cheaper to send someone out to read the meter than using a meter with telemetry and avoiding the home visit.

Your friend's confusion may arise from the fact that the mains supply frequency is sometimes used to maintain a clock once it is set. This was very common when clocks used synchronous motors, rather than electronics. The long term accuracy is excellent (better than quartz), although it can vary a bit over short periods as the frequency can fluctuate with the load on the power grid.

In theory you could still do this with electronic clocks, but I doubt anyone bothers now that quartz modules are so cheap, and can be periodically corrected using information in the digital TV bitstream (and in the teletext pages on analogue TV).

There are several other ways of setting the time - Internet time servers, MSF clock (formerly at Rugby, but now moved to somewhere I can't be bothered to look up!), GPS, DAB...

http://www.npl.co.uk/server.php?show=ConWebDoc.998

Yes, it gets the time off information carried in the same way as analogue teletext - which works fine via SCART.