Our line length function is based on the average width of all 26 uppercase
characters from A-Z of the selected font. There is also a Lower case average
that is used when you use all lower case or mixed case.  The accuracy gets
better as the number of characters increases. For instance, the letter "W"
on its own is the widest of all characters, the letter "i" the smallest. These
characters will be counted as the same length in the estimator when in fact
they would be vastly different in the real world. Therefore, a phrase that has
a lot of wide characters like "MOM" will be wider than estimated whereas the
phrase "Jill" will require less space than estimated. However, for phrases
where the letters are well mixed the estimate will be fairly close.