An  Accurate  Clock

Well, nearly.  The US government set up a website some time ago that displays a real-time clock that is linked to an extremely accurate atomic clock.  The time displayed is accurate within limitations stated on that site - there is a slight error in the display owing to the small amount of time it takes for information to be sent over the Internet.  It also includes a nifty World map that shows which areas are in daylight and which are in darkness.  However, as it stands, it only shows the correct time for US timezones, though it can also display Universal Time.

Unfortunately, they saw fit to modify timezone.cgi (the 'active ingredient') during 2007 such that it will now only work with US timezone names (or UTC) as the 'zone name' argument.  This has considerably reduced its usefulness outside the US, but for those within the GMT timezone, which includes the UK when not in 'Summer Time' (that is, unless the UK government meddles with it), it gives the correct time when UTC has been selected.

Meanwhile, I have found a far more useful site (www.timeanddate.com) that will display a similarly accurate clock with a wide choice of presentations.  It will work in all time zones and can display in a variety of languages, plus it can be embedded as an IFRAME in any web page (see above).  More information here.

As a result of changes to the US government's site, the JavaScript I wrote in 2005/6 that made its clock display properly for other (non-US) timezones no longer works - it just gives an error message.  I regret that I can no longer give you a clock using the US site that displays properly for all timezones, but I provide the following links that will give a display in UTC (which is essentially the same as GMT) - this is probably more useful for European users.

I have commented out my original JavaScript so it is inactive, but you may still view the source.