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You just finished running a race, but your watch disagrees with the official distance and timing. Which should you trust? While race organizers can screw up their distance or timing, they usually don't. Let's look at how races are measured and why they may disagree with your watch—which happens more often than you might realize.

How races measure your time

Before we compare a watch time to an official race time, we need to know what kind of official race time we're looking at. There are two different numbers you might see from a race: gun time and chip time. They may differ from each other and from your watch. Here's where each comes from:

Chip time

Chip time , also sometimes called net time , is the time from when you personally cross the start line until you personally cross the finish line. This is the time that matters for most of us.

Chips measure your personal start and finish because big races often have a crowd at the start line.…