The seat and back rest are rigidly joined together and carried by a frame (4) which is supported by a pivoted clamp bolt (5) at the back rest end and by a pivoted support arm fixed to a support tube (7) which carries a sleeve (8) in which the clamp bolt (5) slides. The clamp bolt can be arrested in any desired position by spring loaded slide blocks (11) tilted by a toggle roller (13) fitted between them. A hydro pneumatic spring unit is recommended between the subframe and the seat to keep the seat in its principle position. The pivot position could be arranged below the seat surface at the rear edge, in which case adjustable feet supports would be required.
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