I've written a tool to convert FIT files to GPX some years ago which does not work with the newest generation of Garmin devices.
The FIT files seem to contain the message type 327 (0x147) which is not seen on the latest list (Profile.xlsx in the FitSDKRelease_21.84.00 archive). So I am unsure if the list is incomplete or I forgot to implement something in my code (still investigating if anything has changed in newer FIT file definitions)...
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Hi Dreuw,
thank you very much to share these message numbers.
I found 2 additional numbers, related to Garmin devices (Garmin Edge 1000, Garmin Edge 1030, ..).
A Locations.fit inside a Garmin Edge contains waypoints (with name, latitude, longitude, altitude, ..) and these waypoints will be displayed on the map.
The message number for these waypoints is 29 (to read and write such a Locations.fit) 
And if somebody wants to add new waypoints to a Garmin Edge, it's possible to decide, how a Garmin Edge should add these new waypoints to an existing Locations.fit:
With message number 189 you can decide it (byte field value):
0 => waypoints will be added to existing waypoints
1 => waypoints will replace all existing waypoints
2 => all existing waypoints will be deleted (very usefull to clear all existing waypoints on an Edge (limited to 200 waypoints) without deleting each waypoint with 5~6 clicks on the display 
)
Best regards
Roland
