For workouts that have different types of intensity data (power, heart rate, or pace), you can choose which of those channels is used to calculate TSS for a given workout. This can be useful for trail running, where rTSS may not accurately reflect the difficulty of a workout, or if a workout has bad power data and you don't want to delete the entire power channel. You can change the TSS calculation source to any available recorded data channel by clicking the arrow next to the TSS field in the workout quickview. The selected TSS value will be used in the weekly summary as well as the PMC and other Dashboard charts.
Note - changing the source of the TSS calculation will use your current threshold settings, so if you change the TSS selection on an older workout and your threshold has since changed, you may get a result that isn't accurate for that point in time.