I've been asked to display the 'correct' time on our website which I frankly feel is rather pointless as 'correct' can be interpretted in such a variety of ways.

Our current method definately results in an inaccurate time as it uses a server control rendering JavaScript that runs onload using the datetime from the server as a parameter to create a clock object in JavaScript that finally renders on the page and then starts incrementing the clock. Between the server processing, network latency and client-side performance (there's plenty other stuff running onload) the clock ends up way off the actual server time and who knows pared to the client PC.

So to get the 'correct' time shown I could;

• Use local PC time and pass new Date() to the JavaScript clock object. Pros: Should be as close to the PC clock as possible. Cons: Not sure how accurate the PC clock is let alone in which timezone.
• Use web service for TCP request to NTP server to update clock on web page. Pros: If local PC also sync'd to NTP will be accurate and best possible match. Cons: Will have to handle all the timezone adjustments relative to our servers. If PC clock is out will still have mismatch.

Do I implement my own web service or use something like; Earth Tools or World Time Web Service (EDIT: link removed - now 404)

Here's a blog post from Jon Galloway on Atomic Clock Web Service which is pretty old and yet ranks high when I google and he doesn't reach a conclusion.

Hoepfully I can win the argument with management why syncing to our server clock (GMT) doesn't makes sense if your not in that timezone and why we even need to match a local PC.

Any angles on this I'm missing?

I've been asked to display the 'correct' time on our website which I frankly feel is rather pointless as 'correct' can be interpretted in such a variety of ways.

Our current method definately results in an inaccurate time as it uses a server control rendering JavaScript that runs onload using the datetime from the server as a parameter to create a clock object in JavaScript that finally renders on the page and then starts incrementing the clock. Between the server processing, network latency and client-side performance (there's plenty other stuff running onload) the clock ends up way off the actual server time and who knows pared to the client PC.

So to get the 'correct' time shown I could;

• Use local PC time and pass new Date() to the JavaScript clock object. Pros: Should be as close to the PC clock as possible. Cons: Not sure how accurate the PC clock is let alone in which timezone.
• Use web service for TCP request to NTP server to update clock on web page. Pros: If local PC also sync'd to NTP will be accurate and best possible match. Cons: Will have to handle all the timezone adjustments relative to our servers. If PC clock is out will still have mismatch.

Do I implement my own web service or use something like; Earth Tools or World Time Web Service (EDIT: link removed - now 404)

Here's a blog post from Jon Galloway on Atomic Clock Web Service which is pretty old and yet ranks high when I google and he doesn't reach a conclusion.

Hoepfully I can win the argument with management why syncing to our server clock (GMT) doesn't makes sense if your not in that timezone and why we even need to match a local PC.

Any angles on this I'm missing?

• javascript
• web-services
• timezone

• What is the purpose of the clock? What resolution is required? Seconds? Minutes? Is the display for the client side local timezone? – Ken Gentle Commented Oct 28, 2008 at 17:54
• I run everything on UTC, personally, especially on servers: If you post the time as 13:47 UTC, there's no confusion. For that matter, neither is there with eBay's system of using PT for everything. – warren Commented Oct 28, 2008 at 18:31

5 Answers 5

I needed to show the accurate time to clients in an auction web app. You can send the current server time with the page and have the javascript initialize right away without waiting for the rest of the page to load. So the, you only are dealing with network latency which in the worst case is not likely to be more than a couple of seconds.

After that, you're pretty darn close to accurate time. As long as your Javascript timer code is written properly, you're not going to far out of sync before the next page load. But I have seen a lot of bad JS clock code. (Hint: Date() good, setTimeout() bad.)

If you have an application that users are going to be sitting on for a long time, just refresh your time sync either by reloading the page or Ajax.

I wouldn't worry about time zones, just use UTC time so there is no confusion about what time things will happen.

First, be certain that your client is aware that Windows, Linux, and OSX all have built-in clocks that are almost always visible to the users (or made visible very easily). Also, be certain that your client is aware of physical clocks that are often located near any kiosks that might be setup to hide the built in clock from the operating system.

If you know that, and your client still wants a clock on your website, have your client define "correct" time, then implement the solution that matches their definition (both of your solutions seem like they would take care of the two most-likely definitions).

you can use geo targeting to know the physical location of a website visitor and in your database stored the (GMT - XX:XX) of the zone and then calculate the time based on the location of the request. that is going to save the long trip to any third party web service.

Another way you can implement it is using IP Geolocation. There are services that can tell you where your user is connecting from based on it's ip (usually including their timezone) and bining that information with your server's realtime clock you can show the user it's local time.

It's far from perfect, specially with corporate users that might seem to be connecting from somewhere they are not (I live in Argentina, but my work internet connection is trough my employeer that is an American pany, so every website assumes I'm located in the US)

Handle time in UTC.

• Have users tell you what zone they want to use.
• If your users have persistent profiles, persist the choice.
• Always display UTC and Local Time side by side and clearly labelled.

You can also display an arbitrary number of user specified zone clocks. Vista does this and I remain surprised at how handy it is.