Even the most careful carpenters can't always make up for crooked materials every time. In fact, few walls in homes are completely square or plumb. Add the fact that houses are constantly shifting, even if you can't see it in your foundation, and you have the need for scribing skirting boards around cabinets and other woodwork. Scribing is the process of trimming a skirt board, also known as a scribe, to make up for minor unevenness in floors, walls and ceilings to create a tight fit for your cabinets and other items.
Set the cabinet in place, level it and anchor it down before marking and cutting scribes. This allows you to see the areas where your walls, floors and woodwork do not perfectly match up. Don't worry, it's perfectly normal for a wall to be 6 mm (1/4 inch) out of line at any given point. Also look for cracks that have widened or recently appeared; they can be signs of major foundation trouble that is best corrected by a professional.
Select a skirt board. It should have the same stain or finish as your cabinets to help it blend in. Cut it to the height of the space under the front edge of your cabinets, typically 8.7 cm (3 1/2 to 4 inches), plus 2.5 cm (1 inch). Cut it long enough to span the whole run of cabinets from side to side.
Tape a sharp pencil to the side of a 2.5 cm (1 inch) dowel rod with its point protruding beyond the end of the dowel. Set the skirt board against the face of the cabinets standing on edge. Starting at one end of the run, drag the dowel along the floor with the pencil on top so the pencil point inscribes the outline of the floor against the face of the skirt board. Run the entire length of the skirt board.
Cut along this line with a jigsaw. Be careful to trim as close to the line as possible. Sand the edge smooth with sand paper by hand and tap it into place underneath the front edge of the cabinet with the flat edge up against the bottom edge of the cabinet and the scribed outline resting tight against the floor.
Make any adjustments with a rasp or coarse sandpaper to get a good fit. Nail through the face of the skirt board into the base of the cabinet to hold it in place. Run a bead of clear silicone caulk along the bottom edge of the scribed skirt board to seal it to the floor. This will prevent dirt and moisture from building up under the edge of the skirt board.
A compass can also be used to achieve the same technique, though it can be more difficult to get consistent results. Try both and use the one that works for you.