Follow the transition between working positions
Observe how a person moves from desk work to reading or conversation. Armless office chairs with headrests should be assessed across those transitions, since headrest contact and arm position may change with the activity. Ask users to describe when the headrest is useful and whether it influences where they sit. Check any available headrest adjustment directly. Avoid asking people to adopt an unfamiliar posture simply to make contact with it. The comparison should establish how the feature relates to their work, including the positions they naturally return to during a typical session.
Trace arm position back to the workstation
The absence of armrests leaves the workstation arrangement especially relevant to forearm placement. Look at the desk edge, keyboard location and space used for documents or other equipment. Ask users to demonstrate their normal tasks rather than holding a pose for inspection. Office chairs need to be assessed at the distance from the desk that people actually use. Record whether they can reach comfortably and where their arms rest. Include the effect of desk obstructions or restricted access, because those conditions can change the seating position during everyday work in the room.
