Pacer Support Guide · Part 13 of 33
Pacing With a Watch: Compass and Steering Wheel
Average pace is your compass, lap pace your steering wheel. Plus: why your watch measures the race longer than its official distance — and what that means for your pace.
Marcel Lennartz
2 min read
Used correctly, the watch is a powerful tool. Used incorrectly, it causes nervous, uneven pacing. The key is to show the right information and to understand what each number means.
Recommended data screen#
| Data field | What it tells you | How to use it |
|---|---|---|
| Instant (current) pace | Your speed over the last few seconds. GPS noise can make it jump by 10–20 s/km. | Do not use it for pacing. Remove it from the main screen. |
| Lap pace | Your average pace in the current 1 km auto-lap. | Your steering wheel: glance at it every few hundred metres and make small corrections. |
| Average pace | Your overall average pace since the start. | Your compass: check it at every auto-lap. This is the number that must be correct at the finish. |
| Elapsed time | Time since the gun. | Compare with the planned cumulative time at official km markers. |
| Distance | GPS distance since the start. | Compare with official km markers to detect GPS drift. |
Set auto-lap to 1 km, disable the lap key and Auto Pause, and use the most accurate recording settings (see the watch checklist and Garmin settings). Do not stare at the watch: a quick glance at lap pace every few hundred metres and a check of the average pace at each auto-lap beep is enough.
Why your watch pace differs from the official pace#
Race courses are measured along the shortest possible line. Runners – and pacers – rarely follow that line exactly: they weave through crowds, go around water stations and take wide corners. Combined with normal GPS error, this means a watch almost always measures a race longer than its official distance.
If you run exactly the official pace on your watch, you will therefore finish late. For example, a 4:15 marathon pacer who runs 6:03 min/km on a watch that measures 42.6 km finishes in about 4:17:44 – almost three minutes late.
Effect of GPS over-distance (full marathon, 4:15 target)#
| Watch measures | Over-distance | Watch pace needed for 4:15:00 |
|---|---|---|
| 42.195 km | 0% | 6:03 min/km (official pace) |
| 42.40 km | ≈ 0.5% | 6:01 min/km |
| 42.62 km | ≈ 1.0% | 5:59 min/km |
| 42.83 km | ≈ 1.5% | 5:57 min/km |