Proper alignment along many different planes is critical when installed into a rough opening. The product must be square, level and plumb to ensure a uniform finish, prevent water infiltration, and allow proper operation of moving parts and prevent premature failure.
Square: It must sit freely and squarely in the rough opening. Any pressure at any point on the frame can push the unit out of square and compromise the seals, put stress on the glazing to the point of fracture and impede movable components.
Level: When the exterior door is level along the horizontal axis no water pockets will be created in the frame of operating parts and the visual lines will be in sync with the other lines of the house. When it is level along the vertical axis, all the seams around the interior perimeter of the frame will be uniform.
Plumb: When properly plumbed, or level from top to bottom, the integrity of the sill slope on exterior doors and patio doors is maintained so they can shed water as designed. When skylights are plumb, the integrity of the slope is maintained so it can shed water as designed. All weatherstripping will also engage properly and moving parts will operate correctly.