Hi!
Recently, friend of mind requested me to write data field for his mind-blowing (for me, at least) upcoming 100 km run. He wants to finish it in 14 hours, so he wants to see a required pace calculated during the race.
My first suggestion was to use built-in 920 feature of Train->"Set Target", but it has quite stupid limitation of 8 hours, which is especially funny when you can set distance limit to 999.95 km. So, perfect use-case for custom data field.
Code is very simple and the whole project is here: https://github.com/Shmuma/garmin-public/tree/master/ultrapace
As there is no way to make customisation in data field's options, 100 km and 14 hours are hardcoded.