Swimming watches: lengths, distance and GPS are different measurements
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Ask how distance was calculated first
In a pool, a watch may estimate distance by counting lengths and multiplying by the configured pool length. In open water it may use GPS and a different process. These are different environments and modes: a reading is not a certified course measurement. Garmin Swim 2 is the documented example here, not a description of every watch. [1]
Pool: configuration and length detection
The Swim 2 manual asks for the correct pool length and describes automatic interval and length detection. It suggests a strong wall push-off and glide before the first stroke. Count errors or an incorrect configured length change distance and pace: verify the measurement before interpreting it as improvement. [1]
Arithmetic example: 40 completed 25 m lengths total 1,000 m. The same 40 lengths with an incorrect 50 m setting become 2,000 m in the calculation. That does not show that speed doubled.
Drills: manual logging where supported
The manual includes drill-log mode for entering drill distance manually. Not every drill produces movements recognisable as normal swimming. Before comparing technique work with a continuous swim, check which parts were recorded automatically and which were entered. Verify modes and controls on your own model. [1]
Open water: acquire the required signal
Swim 2’s open-water mode calls for satellite acquisition before starting. This does not prove every track is exact, or make GPS interchangeable with pool-length counting. Start procedure, route, conditions and recording mode belong alongside any data comparison. No universal error margin is assigned here. [1]
Use the number without chasing the device
- Check pool length and selected mode.
- Separate rests, drills and continuous swimming when comparing pace.
- Record a doubtful count rather than treating it as a record.
- Use consistent testing procedures to assess performance.
For a critical-speed test see CSS. Time over a verified distance answers a different question from an efficiency score or a session’s estimated distance.
Sources and limits
- Garmin Swim 2 Owner’s Manual. Model-specific manual, copyright2019. Not an independent comparison or validation of all watches.
Sources checked on 29 October 2026.