The perpendicularity test instrument (PERTEST) allows practically, quickly and directly to survey perpendicularity and straightness errors with the lowest tolerance. No tare, squares or cubes are required. Pertest is always ready to be used since the structure in granite and the working precision assure stability and repetition. The sliding of the gauge stand (not supplied) is on air bearings as for the movement on the base in order to avoid all friction and wear causes. The gauge is moved up and down by pushing a button; moreover Pertest is provided with filtering and regulation unit for the compressed air.