What is the purpose of a level when installing a cabinet or shelf?

LEVEL USE IN INSTALLATION ensures that horizontal surfaces are truly horizontal (perpendicular to gravity) and vertical elements are truly vertical (plumb). WHY IT MATTERS FOR CABINETS AND SHELVES: FUNCTIONALITY — cabinet doors on unlevel cabinets swing open or close on their own due to gravity; drawers bind or slide; items on unlevel shelves slide or tip; AESTHETICS — even a small deviation from level is visible to the eye, especially with long runs of cabinets; ALIGNMENT — in kitchen installations, all upper cabinets must be level with each other and lower cabinets must be level for countertops to fit correctly. INSTALLATION PROCEDURE: (1) Find the high point of the floor or wall along the installation run (floors and walls are often not perfectly level); (2) Use the high point as the reference for the first cabinet; (3) Shim subsequent cabinets up to match the first if needed; (4) Check level in both dimensions (side to side AND front to back) using the level; (5) Secure the cabinet at the shimmed position. LEVEL TYPES USED IN INSTALLATION: 4-foot carpenter's level for long runs; 2-foot level for individual units; torpedo level for tight spaces; laser level for long installations or finding reference height across a large area.