Backwards Compatibility.  We worked closely with Milgard's engineers to understand the limitations of the existing mechanism inside the door.  As a result, we were able to radically change the way the handle worked without changing the internal mechanism at all.  This is important for two reasons:  it saves Milgard on inventory, development time and money, and it allows the end customer to leverage their current investments and upgrade the usability of their Milgard door in a matter of minutes using just a screwdriver.