When you use ARCHICAD to create building models, you learn pretty quickly that thinking about the direction of a Wall and it’s Reference Line is pretty important.   

Very often you spend a lot of time violently throwing the mouse from one side of the screen to the other just to change the Reference Line position of a Wall… without that, inside ends up out and vice versa!  

This can be pretty annoying - but can easily be solved with the help of a couple of shortcut keys!