Anthropometrics: Important Aspects of Users’ Bodies - Foundations for Designing User-Centered Systems - page 65

Fig. 3.9 A screen shot of an application (Word11 for Macintosh) with several menus

Fig. 3.10 Word 2010 for Window's menu bar with offset from display edge

Figure 3.9 shows several example menu bars. The top menu (starting with the
Apple and Word) will be the fastest because it is next to the screen edge. Being
next to the edge makes the target size very large. The other menus below that will
be slower to access. The icons on the far left (the dashed box with a pointer, the
grid, the circular line, picture, etc.) will, however, be relatively fast to point to,
because they are on an edge, if the user is approaching them from the center of the
window. However, they are not because they are offset from the edge by Word.
Figure 3.10 shows Word 2010's menu in Windows in which the menu items
(File, Home, etc.) are offset from the top edge. The time to switch to a menu bar
item in Fig. 3.9 is (assuming from the middle of the screen) limited by the constant
time and time to click because the target size is infinite, so the user can move the
mouse without regard to the target. So, about 100 ms + 1,100 ms or 1,200 ms. The
time to switch to a menu bar item in Fig. 3.10 is about 100 ms + 100 ms 9 log 2
(8 cm/1 cm) or 1,500 ms. In other words, at least 25% longer.
Figure 3.11 shows the Eclipse integrated development environment (IDE),
including some aspects for writing user models. In this interface the menus are also
offset from the top of the window, which might not even be flush with the top of
the display. Selecting buttons and panels will thus be slower and more error prone
with this menu.
Fitts' law yields some more sophisticated suggestions when combined with
Hick's law, which predicts how long it takes to choose one item from a list of
several options (Landauer 1987a ). When combined, these two laws suggest that