steering transmission where a part of the steering forces is transmitted by purely mechanical means and the other parts either by: ... hydraulic or mechanical/hydraulic or ... electric or mechanical/electric or ... pneumatic or mechanical/pneumatic means. In either case, where the mechanical part of the transmission is designed only to give position feedback and is too weak to transmit the total sum of the steering forces, this system shall be considered to be purely hydraulic, respectively purely electric, or purely pneumatic steering transmission