In the settings you can...
Set your next batch number
Change general formulas for ABV, FG and IBU calculation
Change units between Metric, US or Imperial
Enable/disable special features
Change units for color and pressure
Activate Power-ups like SmartPID, Tilt, iSpindel, Brewpiless, MyBrewbot
Export all your personal data for local backup in a JSON file
Reset included data back to its default values
Reloads the application, usefull if you want to refresh to make sure you got the latest version of the application.
Normally this is activated by default, except on iOS (iPhone / iPad) where it is deactivated due to issues that Apple introduced in iOS 12.2 (will be activated by default again when this is fixed by Apple).
When active, all your data is cached persistently in a local database for offline use and synchronized when you get back online.
When deactivated, your data is cached in local memory, but is not persistent across application reboots.
This must be kept off unless you experience issues where the device is not synchronizing at all on your current network, example some corporate networks. Setting can be activated to be used to work around proxies that prevent the Brewfather client from connecting to the backend. Activating this will decrease performance somewhat.