... JB/T7974-99 , rib type or case type ,recangle/round surface , working surface made by skiving ,groove V/T/U shape and hole ... for testing and drawing of work pieces on it ,The surface plate shall be adjustable to horizontal positaion and laded evenly ... (20±5),and vibration shall be avoided when using granite surface plate specification:Type(mm)Precision Grade(μm) 123Final Machining2000*1000203996 ...