When editing a / Sound in the Screen, 1 is labeled I/II
and can be used to access the parameters of both parts. A square with two part indicators show which part is in focus.
On the User Interface there is a colored frame around the main area including an indicator for the selected part. A touch/click on the indicator opens the parameters of the other part.
By default, both and User Interfaces share the same part focus, meaning that part selection is reflected everywhere. However, the User Interface has its own part focus and can ignore part selections in the User Interface, if explicitly enabled in the system settings, see chapter Setup (C15 System Settings).