Why is my tablet unknown?

For GNOME to initialize a tablet with the correct capabilities such as pressure, tilt, mapable buttons, etc. it needs to first know which capabilities are available. This information is not provided by the devices but resides in a static device database provided by the libwacom library. Devices must be individually added to this database and thus may not yet be available in the version of libwacom provided by your distribution.

If a tablet is not supported by libwacom, GNOME cannot know which capabilities are available. GNOME then defaults to assuming the tablet is built into one of the outputs (the built-in one if available) and it has no external buttons. The pen (stylus) tool defaults to a standard two-button tool. This usually has little effect on the functionality of the tablet but it does limit the configuration of the tablet.

For instructions on how to add a device please see the instructions in the libwacom repository.