The model: Load, licence plate and view

Four requirements, four reasons. 1) LICENCE PLATE: plate front and rear clearly readable, not screened off (Book p.203). 2) LIGHTING: lights and retroreflectors clearly visible, not covered (Book p.205). 3) VIEW: all mirrors usable, unobstructed view out (Book p.204). 4) TRAILER: if it hinders your rearward view through the normal outside mirrors, extra outside mirrors are required (Book p.230).