Introduction: With the rapid evolution of mobile devices, there is also a tremendous growth in their applications. This triggers new research on more efficient techniques of human-computer interaction. To point at an object of interest seen on the screen of a mobile device, various new methods were suggested recently.
Methods: This paper presents the results of a user study that employed tilting as a technique for entering text. The independent variables in the user study were mobility (sitting, walking, sitting in the moving bus) and keyboard size (5×3, 10×4). The experiment involved 50 participants aged from 22 to 65.
Results: In the walking condition, it took on average 11.3% more time for participants to complete the task compared to the sitting condition with 5×3 keyboard, and 45.1% more time compared to the sitting condition with 10×4 keyboard. Keyboard size had a marked influence on task completion time. In addition, task completion time while traveling by bus was 3.2% longer than that observed for the walking condition with 5×3 keyboard. Surprisingly, task completion time with 10×4 keyboard while traveling by bus was 10.4% shorter compared to the walking condition. Error rate and movement efficiency were investigated additionally to find out the explanation for such performance data.

Keywords: mobile text input, tilt input, keyboard size, performance measurement