text width={\qfdWhatW - 0.2}cm doesn't parse — the braces don't
evaluate the arithmetic, so TikZ sees "4.6 - 0.2cm" which isn't a
valid dimension. Pre-compute the narrower width with
\pgfmathsetmacro and reference the resulting macro instead.
text width={\qfdWhatW - 0.2}cm doesn't parse — the braces don't
evaluate the arithmetic, so TikZ sees "4.6 - 0.2cm" which isn't a
valid dimension. Pre-compute the narrower width with
\pgfmathsetmacro and reference the resulting macro instead.