Speaker placement question-

When I read a a review of whatever speaker, the reviewer may comment how far the speakers were placed from the back and side walls. I have always wondered how is this measured. If its a box speaker, as most are, and if the speakers are said to be 36" from the back wall, is that 36" measured from the speaker's back panel, the front panel where the drivers are mounted, or from a point at the center of the speaker cabinet? Same question applies to distance to the side wall. Thanks!