Abstract: A chair back support arrangement of a type including an upright supporting a back support arranged to slidably engage the upright, and interlocking means to maintain a selected support height for the back support, the interlocking means including a rack either affixed to or being part of the upright an engaging member supported by the back support and arranged to selectively interlock with the rack and being able to be activated to effect a change from interlocking to not interlocking by a change by relative positioning of the back support with respect to the upright. A catch is supported by the support back so that in one position, it can catch and hold in a non-engaging position, the engaging member clear of the rack, and in another position, it will release such engaging member to effect an interengaging action with the rack.

Abstract: An adjustment mechanism for a chair that adjusts the angle of inclination of both the seat and back portions simultaneously to adopt the best relative ergonomic positions. The adjustment mechanism comprises a mounting means for connection to a chair support column and a first frame member for supporting the seat portion that is pivotally mounted to the mounting means. A second frame member for supporting the back portion of a chair is pivotally mounted to the first frame member. A control member is pivotally mounted at a first end to the second frame member, and has a slot that engages a bar that is fixed to the first frame member. Locking means associated with the bar releasably locks the control member with respect to the bar. A link is pivotally attached at one end to the second end of the control member and is pivotally attached at the other end to the mounting means. The control member is held by the link so that the angle of the slot to the horizontal is maintained.