Vim (window-resize): how do I easily make the windows equally high for only one column?

I have a vertically split window and the window is further horizontally split within each column. I want to make the height of the windows within one column the same, but do not want to change the heights within the other (let's say, one window in the other column is set to highest possible, like by using CTRL-W_, and I don't want to change that). What is the easiest way possible to accomplish this?