Measure The Relationships That Cannot Change
The first comparison should identify the dimensions that the user cannot alter through these two features. With fixed-depth office chairs with fixed armrests, record the usable seat depth and the arms' position relative to the seat. Check their spacing and their relationship to the desk opening. Measurements help explain differences between seating arrangements, but they need a seated trial to establish practical fit. Do not assume that similar overall dimensions produce the same experience. The user needs to test the backrest, seat edge and arm supports as a connected arrangement during their ordinary work activities.
Examine Seat Fit Without Repositioning The User
Ask the employee to sit with their back against the backrest and their hands in their normal working positions. Observe where the seat ends beneath the thighs and ask about contact near the backs of the knees. If the user slides forwards, establish why before treating that position as acceptable. Office chairs without seat-depth adjustment cannot be shortened through a depth control. The trial should establish whether the existing seat dimension works while the person uses the backrest, rather than relying on a posture adopted to avoid the front edge or reach around an obstruction.

