shelf mechanism 1 to the underside of the desk can also be used swivel bracket 32 is attached to swivel bracket assembly 33 3 and mounting bracket support 6 by means of a rivet not shown a large washer 35 is fitted between swivel bracket 32 and mounting bracket 3 the washer may be made of any number of an upwardly extending piece to permit attachment of link means the vertical profile of the overall mechanism can be shortened increasing the leg room available to the user when the keyboard is positioned beneath the desk thus another aspect of the present invention is the attachment of an auxiliary shelf or keyboard shelf to a desk top so that the auxiliary shelf can move both horizontally and vertically relative to the desk top the attachment being made so that nothing extends below the bottom of the auxiliary shelf this arrangement maximizes the amount of leg room beneath the auxiliary shelf the attachment between the auxiliary shelf and the desk can be made by either a parallelogram linkage or by a non parallelogram linkage or by a linkage of the type described in detail in this application i e upper arm side arm stopping means one means by which this type of attachment may be accomplished is by using an auxiliary shelf with a vertically oriented piece attached to its rear side the linkage can be attached to this vertically oriented piece precluding the need for anything.