Albus made the correct wand-movements as he incanted "Fideliusil sprairm rektangoobek." A glowing-blue twelve-foot-by-ten-foot rectangle appeared. Interestingly, when Albus looked at Number 11 Grimmauld Place, Albus saw in his peripheral vision that the glowing-blue rectangular laid on the front of Number 13, as if the glowing-blue rectangle were sticking-charmed to the building; but when Albus looked at Number 13, the glowing-blue rectangle shifted sideways to cover a twelve-foot-by-ten-foot rectangle of Number 11’s front wall, which Albus saw only with peripheral vision.