The MENUBARHEIGHT function returns the height of the menu bar.
The SCREENVISIBLE function returns the coordinates of the visible area of the screen, which excludes the menu bar and the dock area.
Note that at least on my Mac, SCREENVISIBLE(Main,Top) + 1 == MENUBARHEIGHT().
I'm not really sure what you are trying to do, so I don't really know what a simpler method might be.