Seat-back definition
Seat-back means the part of the seat that is almost vertical, designed to support the passenger's back, shoulders and, possibly, his head;
Seat-back means a structural element behind the seating position’s R-point at a height of more than 450 mm measured from the vertical plane passing through the R-point against which the back of a seated person can rest completely;
Seat-back means the part of the seat that is almost vertical or at the angle specified by manufacturer, designed to support the passenger’s back and shoulders.”