# How to calculate "badness" for ragged right margins?

In TeXbook (p.30) it is said:

When \raggedright has been specified, badness reflects the amount of space at the right margin, instead of the spacing between words.

That is, in ragged-right case, badness is difference between required and actual width (not 100*r^3). In the following example badness must be stretchability of rightskip (i.e., 2em), so considering that 1em is 10pt, badness must be 20, but badness 100 is output. Why?

\hbadness=-1 % to report the badness
\raggedright % \rightskip 0pt plus2em \spaceskip.3333em
\def\text{The badness of this line is 1000.}
\setbox0=\hbox{\text}

The comment just means that the only stretch glue is at the right not between words, not that a different calculation is being used, badness 100 means stretched by cube root of 100/100 which is a factor of 1, so basically you are just seeing the effects of rounding error. In other words, badness is (20/20)^3*100.