Races are generally scored with one of two methods: Chip Timing, and Tear Tag Scoring. Here's how they work:

Tear tag scoring involves a bib number with a tear off strip at the bottom of the bib. Each number is unique, and the race timers have a list of who belongs to each number.

Every time a runner crosses the finish line, a race timer clicks a button to record the finish time. The tear-off tags are collected in the order that the runners finish. The recorded times are then matched up with the tags, providing a time for each runner.

As a method of double-checking, selected runners' times are also recorded. As a runner with a very visible bib number approaches, another race timer types in the runner's number, and then clicks another button as the runner crosses the finish line. This records the specific time for that runner, to help check that the matched times are in sync.

Tear tag timing, though less expensive than chip timing has some challenges, and has more opportunity for error. If a runner has their bib on their back, the scoring person might think the runner is a bandit, and not record a time. If bandits cross the finish, a time might be recorded for them, if the scoring person thinks they have their bib on their back. Sometimes, a runner will finish, and then go back to run through the finish again, with a slower friend, and this can cause problems too.

This is why its important to wear your bib on your front, only cross the finish once, and only cross the finish if you have registered for the event.

Chip timing involves a runner wearing a timing chip, generally on the shoe or ankle, and timing mats. When the runner crosses a timing mat, the time is recorded. A timing mat will be at the finish line. A timing mat will generally also be at the start line too, and in large races, at key points on the course also.

Gun Time is how long it took you to get to the finish after the start of the race.

Chip Time is the time it took you to get from the start line to the finish line. This will vary from the Gun Time if it took you more than a second to cross the start line. In a large race, if you are not at the very front at the start, this can range from a few seconds, to a few minutes.

When mats are at key points in the course, split times will also be listed in the results. In large marathons, like Chicago or Boston, family and friends can get your split times texted or emailed in real time.

Chip timing is generally more accurate, and offers less opportunity for mistakes. However, it is more expensive than tear-tag scoring.

Runners still wear a bib numbers when races are chip timed. This allows race officials to know that a runner is registered for the race, and often which event, when there are multiple events.