Inspection and calibration tools and equipment are used for quality assurance before, during, and after production on the shop floor or in a dedicated QA or metrology lab. Surface plates are used for a flat reference plane for QA, inspection, metrology, and set up applications. Gauge blocks and sets are stacked together to make a desired length. They have two opposing faces that are ground flat at an exact distance apart. Optical comparators take 2D measurements of a part of workpiece. They are commonly used in in machinery manufacturing, including aviation, aerospace industry, watches and clocks, electronics, and in research and detection metering stations. Bench centers are mounted to a table and support a workpiece for inspection and/or calibration.