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What is Critical Swim Speed? | Garmin Customer Support
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https://www8.garmin.com/manuals/webhelp/GUID-F41EAFB3-6CC9-42DE-9C6C-9E358DBB0671/EN-US/GUID-F9FFE0BF-ED46-40D4-A562-92F1CB4C3650.html
Forerunner 265 Series Watch Owner's Manual - Recording a Critical Swim Speed Test