You can now map custom activity fields to fields in messages in activity FIT files. This is where summary information about the activity is stored. The field is automatically populated with data from the FIT file if it is present. The default behaviour is to look in the session record for a matching field name or number. However you can prefix the field name/number with the name/number of the record to search in other records.
This is what the session looks like on fitfileviewer.com.
You need to re-process existing activities after adding a field:
You can do this in bulk using the activity list view:
If set the FIT file session field name is also used when the field is written to a FIT file.
Examples of non-session record fields;
activity.total_timer_time-
140.4(field number 4 of message number 140, Garmin Venu watch training effect times 10)
The script of the custom field can be used to transform the value once it has been read:
activity.isNew ? activity.TrainingEffect / 10 : activity.TrainingEffect
This expression only does this when the activity is new or its file is reprocessed otherwise it returns it as is.
If the field has multiple values you can use array index notation to extract the one you want:
avg_left_power_phase[2]
To get the 3rd value (first has index 0).