Evaluation of Callout Design for Ultra-small Touch Screen Devices

Ultra-small touch screen devices tend to suffer from occlusion or the fat finger problem owing to their limited input area. Callout design, a design principle that involves the placement of a callout in a non-occluded area in order to display the occluded area, could eliminate occlusion. However, callout designs for ultra-small touch screen devices have not yet been explored. In this study, we conducted an experiment to examine eight callout designs for ultra-small touch screen devices. The results show that the selection speed was higher when the content of the callout was changed continuously, the error rate decreased when a pointer was displayed to indicate the touched position within the callout, and the workload decreased when the content was changed continuously. Further, the score that subjectively evaluates the performance decreased when the position of the callout was fixed.