Add a feature, so that the pen size stays the same pixel amount, no matter how much the user zooms in, similar to how the rubber always looks like the same size.
I am so confused not to have found a lot of this request before, since i really get annoyed of not having this function.
Whenever i zoom in, in order to write something in a smaller space, i would really appreciate not having to change the pen width/size manually.

Besides that i really like your App :)