Synchronized mechanism with backrest return prevention safety function and 3 locking positions; Paddle A is for seat height adjustment, Paddle E is for seat initial angle adjustment, and C is for seat and back movement. The seat initial angle is in the range of -3°～2°, seat angle is 2°～14°, back angle is 90°～110°, Paddle F is for spring tension adjustment, and Paddle G is for seat slider movement with a 58mm's travel.