ABSTRACT
This chapter presents a model of seated postures which examines the changes in seated fingertip height for a set of alternative postural configurations, and argues that these changes require a much greater range of adjustability of keyboard support height than is customarily prescribed by standards and recommendations. Chairs with forward-tilting seat pan angles are explicitly permitted in this standard, but as part of the specific solution, since a range of forward angles is not specified. ANSI/HFS 8.4.1 discusses the location of the forearm in terms of three angles; these are forearm to superior frontal plane, forearm to upper arm, and seat back to vertical. The deviation of the upper arm from vertical will increase the vertical height of the elbow. In addition, decreasing the angle between the upper arm and forearm will increase the height of the wrist and hand.
