2.1.3 Reading The standard text height of 2.20 mm found in many mobile phones is the result of looking for a minimal text size considering the distance between mobile phone and the eyes and the resolution of the eyes and the mobile phone screen.
Darroch et al. [3] analyzed the effect of different font sizes on the reading performance while standing when using the small screen a mobile device provides. Their results show that reading performance did not increase above 6 point (2.12 mm), but the participants actually preferred fonts in the range of 8-12 point (2.82 – 4.23 mm). Barnard et al. [2] showed that a larger font size of 12 point (4.23 mm) when compared with 10 point (3.53 mm) leads to a greater subjective readability, lower levels of perceived difficulty in reading and was also more preferred by the users.
Mustonen et al. [14] analyzed different methods for studying legibility of text displayed on a mobile phone while walking. The main results are that an increase in walking speed leads to a deterioration of visual performance, and therefore, to a lower reading performance. In addition, they compared two different settings in order to study reading performance while walking. In the first one, the participants searched for a number of target characters in a piece of pseudo text and in the second one a realistic passages of text was used which was read by the participants. Their results show that reading a realistic passages of text is a more useful measure of legibility due to the increased external validity as the participants used rather unrealistic approaches to search for and count the target characters when using the pseudo text.