Abstract: This invention is a test apparatus and method for noting whether the axis of sight of an optical instrument is parallel to the axis of a horizontal bubble level of that instrument. The apparatus has: (1) a vertically elongated first scale facing in one direction; and (2) a similarly calibrated second scale closely parallel to the first scale and facing in the opposite direction and selectively adjustable along the first scale. In the present method, first, the optical instrument is leveled midway between two such test apparatuses about 200 feet apart, with their respective second scales facing each other. Using the instrument, readings are taken on these second scales. Then the second scale of one test apparatus is adjusted along its first scale to a position thereon which matches the reading just taken on the second scale of the other test apparatus. Next the optical instrument is leveled at a position close to either test apparatus on the opposite side of it from the other test apparatus.