Now I remember what I meant. This line is problematic. You cannot apply any function on mp_normalizer here (x/100 in this case), because this prevents the outside use from applying an absolute offset. So you cannot tell the user to hold the remote still and then pass the current value via xwii_iface_set_mp_normalization().
And we cannot require the user to apply "x*100" to the values as we want this to be an implementation detail.

I removed the "x/100" now. If this makes the whole computation too static or coarse-grained, feel free to tell me how to change it. However, it works great for me.