My ergonomical M$ Keyboard has this zoom button in between the two key blocks, and it is by default bound to a zoom functionality (which I do neither need nor is it avaliable on my Ubuntu Linux by default). Since scrolling long texts can be cumbersome with the mouse, I looked for a way to reassign this slider to scrolling.

In the gentoo wiki I found a very simple solution: I just needed to change one line (for me it was line 32) in the /lib/udev/rules.d/95-keymap.rules file:

Change it from

ENV{ID_VENDOR}=="Microsoft", ENV{ID_MODEL_ID}=="00db", RUN+="keymap $name 0xc022d zoomin 0xc022e zoomout"

to

ENV{ID_VENDOR}=="Microsoft", ENV{ID_MODEL_ID}=="00db", RUN+="keymap $name 0xc022d pageup 0xc022e pagedown"

And you’re done!