Rotary Encoder to adjust Jog-Speed?

Hi

I build parallel a pendant with a arduino mega.

everything is up.. i can select axis xyz ,select the scale (0.001 0.001 0.01 0.1 1).
I can adjust spindle feed snd rapid overrides.

now is my wish to adjust the speed when i jog.
i done this manual with mouse on desktop..

but i cant find the right hal pin

does someone have a idea ?

thanks!
 

All the halui pins are in the docs
linuxcnc.org/docs/stable/html/gui/halui.html#_joint_jogging