Calculation Error

When Alastair did his computations and got 150% enlargement that set off a
red flag for me. I double checked Alastair's computations and he is right.

Letter spacing should change to 0.045em NOT 0.12em.

My mistake was in using the research percentages applied to whole letters,
not the space between them as the researcher MacLiesh suggested. Thus, our
letter spacing should be applied to the spacing between letters, not to
letters. That is 0.12x0.25=.03em.  There was actually an improvement up to
0.24 of the space between letters. Then the improvement flattened. I did a
linear interpolation from 0 to 0.24 when I got 0.12. I think in this case
the research max 0.06em could make size problems for developers, but the
min 0.03em is a little small from my personal experience, and the research
plots in the MacLeish research. Thus, I recommend linear interpolation
again to get 0.045em.

Word spacing is correct because it is applied to 1em, (a space character
approximately). However when we compute the size increase due to word
spacing we must divide by the average word size (language dependent (about
5 in English usage)).  So, to compute the effect of letter spacing on text
length we should apply the following multiplication factor:
(1+letter-spacing)(1+(1/5)word-spacing)<= (1+0.045)(1+0.32)=1.07844<1.08.

Empirical Evidence: Let us look at an average font like Tahoma. The average
character width is 8.69px including normal letter spacing.

Conclusion:
Word spacing should not change. Letter spacing should change from 0.12em to
0.045em.

Wayne