In an empty buffer, m-: of

(let ((p (point))) (insert " ") (add-text-properties p (point) `(display
(space :width 7))) (insert ".") (current-column))

returns 2 in gui mode but 8 in character mode of emacsen more recent than
emacs 22.  (I tried it in several emacs versions including the most recent
27.0.50 snapshot.)

I discovered this by figuring out why the m-x bubbles game hasn't worked in
character mode since emacs 22.