Huion 420 is an inexpensive graphics tablet and stylus. It can be used to write, mark, draw or sign in Linux apps.
The DIGImend drivers support Huion graphics tablets. The 420 is supported in v5 of these drivers.
If you are using Linux kernel v3.17 or later, these drivers are already merged into it. Huion 420 will work correctly when you plug the tablet in.
If you are using Linux kernel version less than 3.17, then the Huion 420 stylus will appear to move on the display, but it has problems. For example, it will be restricted to the top-left region of the display.
To get full support for Huion 420, download the DIGImend v5 drivers from here. The file to download is named digimend-kernel-drivers-5.tar.gz.
Unzip the downloaded file. Run make to build the drivers.
Remove the existing Huion driver that might have been loaded:
$ sudo rmmod hid-huion
Install the new drivers using sudo make install
Unplug and plug back the Huion 420. You should be able to use the stylus to operate the whole display area, write and draw now.
Tried with: Linux kernel 3.13.0-44 and Ubuntu 14.04