The London Marathon is one of the biggest distance-running events in the world, bringing together people of all ages and abilities on one course.
Such an epic 26-mile undertaking means that entrants need all the support they can get, and thanks to advances in technology it's now a great deal easier to track your friends' progress than it was back in 1981, when the Marathon was born.
So whether you're at home, on the go, or spectating around the course, here are a few tips on how to follow your runners throughout the day.
Official app and online tracker
The Virgin Money London Marathon ran its own mobile app for the first time in 2015, to make it easier for friends and family of participants to track the race as it progresses.
2017 is supposed to be the first year that this service will be available on Android, having previously been an iPhone exclusive.
The tracking facility is also accessible via the official website - though it is currently inactive, pending the race start. Timing intervals are every five kilometres and you can search both by a runner's name and their race number.
The app still appears to be only available on iPhone, so Android users will have to head online or use other running apps.
The official app and online timing uses the chips given to each runner, but only delivers estimated positions every five kilometres. If you want more specific feedback, it is worth exploring other options.
There is a range of other apps available on both Apple and Android that use GPS tracking and automatically deliver live updates to followers online.
These smartphone apps can provide more detailed and personal way to follow a friend than the official website. Set up before the marathon starts, the smartphone will send progress reports via email and social media throughout the race.
Some of the running apps are free, but to access the live-tracking facilities with the likes of Garmin Fit and RunKeeper you’ll have to sign up for the paid subscription service.
To avoid the battery running out mid-race, make sure you pull back to the Home screen so that the app is only operating in the background.
It’s also best to be aware that during past London Marathons, these mobile means of tracking have had problems with overload.
If you’re out on the course looking to spot a specific runner, you can also use good old-fashioned mental arithmetic to ensure you’re in the right place at the right time.
Provided your charge has done a modicum of training – enough that they can take a stab at their average minutes-per-mile – and you know what time they start, you can make a fair guess what time they’ll hit each mile marker around the course.