Extruder size Dialer for Ultimaker 2+ - Olson block

Using an Ultimaker 2+ with the Olson Block, I frequently change my extruder.
As I'm working with several colleague and students, it is a common error to forget which extruder size is installed !

This simple dialer, glued to the side of the printer is a nice reminder of what is installed.

Thanks for the original design (made for X-Wing boardgame manoeuver :p )