So your mate has signed up to run the marathon and the big day is almost here. But trying to work out where they will be based on pace timings is all well and good, but not that practical come race day when you're both in the thick of it. How can you be sure that you'll be at the right point waving your "Keep Going" flag and that they will see it? The answer is incredibly simple: Google Latitude.

Follow our six step guide to make sure come race day you know exactly where your friends are.

You and the person you are going to be tracking have to both sign-up for Google Latitude on your phone.

It's incredibly painless and the service works with iPhone, BlackBerry, Nokia S60 handsets, some Sony Ericsson models, Windows 5.0 and above and Android handsets via the Google Maps application. Basically anything that can run the Google Maps version 3.0+ or higher.

Currently iPhone users have to be logged into the Google Latitude website rather than being able to run the service in the background as iPhone OS 3 doesn't support multitasking.

Now that you've both signed up for the service, let each other track the others whereabouts by requesting and accepting the call to be tracked.

When it comes to race day the runner will have to carry their phone with them. If it's running Google Maps 3.0 or higher then the app can be on in the background, if it's the iPhone then you'll have to be logged into the website via Safari. Don't worry, once you turn it on you won't have to look at it again until you've finished the race.

If you are the follower all that's left to do is watch your friend's icon whizz (yeah right) around the course on Sunday. You'll get a good understanding where they are based on the location of their icon on the map and then be able to get in the right place so they can see you and you can motivate them.

Use the service at the end of the race to find each other, or better still, the local bar.

Remember to turn off the tracking feature at the end of the day or else they will be able to freak you out in 2-weeks time, telling you you've just walked into the local curry house when you're supposed to be training for the next big race.

Good luck!