the present apparatus comprises a manually adjustable tilt control mechanism which permits adjustable control of the front to back tilt of a chair assembly on a support frame , including a chair assembly having a lowermost seat portion , a column and forwardly extending support arm , for supporting the chair seat portion , a pair of dissimilarly sized resilient blocks , disposed between the end of the support arm and the bottom side of the chair seat portion . the resilient blocks may be adjustably compressed or decompressed between the bottom of the seat portion and the support arm , to adjust the tiltability of the seat .