When interacting with a touch screen, users may obscure important information with their hands. The hand movement to access frequently used functions should be minimised by placing these controls in the area of the screen closer to the user.

A Swiss signaller logging on a touch based communications device.

Context

The user needs to position arm and hands to access functions on a touchscreen.

Forces

Requiring the user to hold the arm in the same position for a longer time may cause fatigue, the so-called ‘gorilla arm syndrome’. On touch screens, a portion of the screen is always closer to the user due to the position of the device on the workplace.

Research found out that pointing actions are more accurate on the lower portion of the screen, whereas the upper visual field is better suited to support perceptual tasks in the distance (Po, 2004).

(Po, 2004) Barry A. Po, Brian D. Fisher, Kellogg S. Booth. Mouse and Touchscreen Selection in the Upper and Lower Visual Fields, in Proceedings of the CHI 2004 Conference, 2004.

Solution

Place the most frequently accessed functions in the lower portion of the screen. Place controls used for surveillance and monitoring of data in the upper visual field.

Safety Impact

The probability of covering up part of the screen containing safety-relevant information is minimised. Possible hazards arising from covering up important information, slow or inaccurate interaction, and arm fatigue are avoided.

Usability Impact

Efficiency; error prevention