unity-design team mailing list archive

[David Regev <david.regev@xxxxxxxxx>]

The equation doesn’t break down here because you’re not supposed to put in
∞. Although the edge may theoretically be infinitely long, it’s not in
practice. Any human being aiming at the edge will stop within a certain
distance past the edge. That means that, effectively, *W* is a certain fixed
quantity, which can be determined through testing and seeing how far users
actually travel past the edge. Jef
Raskin<http://books.google.com/books?id=D39vjmLfO3kC&pg=PA94>,
for example, found that *W* was 50 mm for the Macintosh. Using these
methods, Fitts’ Law will get you more accurate results. You can also figure
out how great *D* must be for global menus not to be faster any more (hint:
probably much larger<http://ubuntuforums.org/showthread.php?p=3494680#post3494680>than
your typical large monitor).


On Sun, May 22, 2011 at 16:53, Ed Lin <edlin280@xxxxxxxxx> wrote:

> I'd also argue that while mathematically sound (at first glance) literally
> putting in infinity doesn't give you a realistic result, think divided by
> zero which can break an otherwise perfectly usable formula. Put in a
> ridiculously large "D" and with infinitive "W" you'd get exactly the same
> result (you'd calculate with zero) which doesn't take in account b, the
> inherent speed of the pointer. Clearly the law fails here. Just see the
> derivation: natural number =∞/2 ??  Someone with a bit more math background,
> please chime in.
>