См EN 1335 Class A
Type A office work chair The type A chair is essentially the same as the type B chair with the following additional requirements: Seat depth shall be adjustable. Chairs with non-adjustable seat depth can not be considered to be type A chairs. Seat inclination shall be adjustable. Chairs with non-adjustable seat inclination can not be considered as type A chairs. The seat inclination must be adjustable by at least six degrees. Seat height shall be 400mm minimum and the adjustment range should be at least 120mm. For the type A chairs, adjustments to the backrest are independent of the seat surface.