Mesa Mesa Mesa (Spanish and Portuguese for "table") is the American English term for tableland, an elevated area of land with a flat top and sides that are usually steep cliffs. It takes its name from its characteristic table-top shape. It may also be called a table hill, table-topped hill or table mountain. It is larger than a butte, which it otherwise resembles closely. It is a characteristic landform of arid environments, particularly the Western and Southwestern United States in badlands and mountainous regions ranging from Washington and California to the Dakotas, Wyoming, Utah, Oklahoma, and Texas. Examples are also found
Optical flat is also needed, on which the test can be performed, preventing both the flat and the test-piece from sagging under their combined weight, Often, a precision-ground surface plate is used as a work surface, providing a steady table-top for testing upon. To provide an even flatter surface, sometimes the test may be performed on top of another optical flat, with the test surface sandwiched in the middle. Absolute flatness is the flatness of an object when measured against an absolute scale, in which the reference flat (standard) is completely free of irregularities. The flatness of any optical flat is relative