Device status, activity info, scuba divind specific data etc vs Garmin Descent MK1

The best you can do is derive this data from ambientPressure / meanSeaLevelPressure / elevation / altitude / pressurehistory / elevationhistory so it will require a lot of testing (eg with a pressure chamber) to get this right, plus also note if you intend to release your app to the public that Garmin won't approve it to be listed in the app store (even if you would only target the mk1) (see https://forums.garmin.com/forum/developers/connect-iq/connect-iq-news-announcements/148653-app-approval-exceptions-updated-09-19-2018 )

The best you can do is derive this data from ambientPressure / meanSeaLevelPressure / elevation / altitude / pressurehistory / elevationhistory so it will require a lot of testing (eg with a pressure chamber) to get this right, plus also note if you intend to release your app to the public that Garmin won't approve it to be listed in the app store (even if you would only target the mk1) (see https://forums.garmin.com/forum/developers/connect-iq/connect-iq-news-announcements/148653-app-approval-exceptions-updated-09-19-2018 )

Nice to know :-( Thanks for the answer...
There is such an official widget ("Surface Interval"), and also default descent watchface which reads information i'm looking for from somewhere, but I accept decision of Garmin not to release the documentation. Although my suggestion would be to allow at least limited set of data available for the "public" development.