Mouse VirtualBox USB Tablet on /dev/input/event3
Move the device 250mm/10in or more along the x-axis.
Pause 3 seconds before movement to reset, Ctrl+C to exit.
Covered distance in device units:        0 at frequency 124.1Hz -       |^C
Estimated sampling frequency: 124Hz (mean 93Hz)
WARNING: Max frequency is more than 30% higher than mean frequency. Manual verification required!
To calculate resolution, measure physical distance covered
and look up the matching resolution in the table below
       0mm          0.00in           400dpi
       0mm          0.00in           600dpi
       0mm          0.00in           800dpi
       0mm          0.00in          1000dpi
       0mm          0.00in          1200dpi
       0mm          0.00in          1400dpi
       0mm          0.00in          1600dpi
       0mm          0.00in          1800dpi
       0mm          0.00in          2000dpi
       0mm          0.00in          2200dpi
       0mm          0.00in          2400dpi
If your resolution is not in the list, calculate it with:
        resolution=0/inches, or
        resolution=0 * 25.4/mm

Entry for hwdb match (replace XXX with the resolution in DPI):
mouse:usb:v80eep0021:name:VirtualBox USB Tablet:
 MOUSE_DPI=XXX@124