-is put into a the @code{thickness} variable of a @code{Stem}
-object. This makes stems almost twice as thick as their normal size.
-To distinguish between variables defined in input files (like
+is put into the @code{thickness} variable of a @code{Stem}
+object. @code{thickness} is measured relative to the thickness of
+staff lines, so these stem lines will be @code{2.6} times the
+width of staff lines. This makes stems almost twice as thick as their
+normal size. To distinguish between variables defined in input files (like