Abstract: A special rear vision mirror device and installation which provides and utilizes a continual safety monitoring of the angular relationship between the pivotally-connected tractor and trailer vehicle units of a "semi" (tractor/trailer tandem-connected vehicles). The overall mirror installation, during a semi's turning maneuver, automatically rotates the mirror in a special relation and correspondence to what at each increment of the turn is the angular relation of the tractor and trailer, particularly the angular changes from a straight (in line) tandem vehicle relation, occurring while the semi is in the turning maneuver. This provides, continuously, a controlled, and as needed, continuously-adjusted safety setting for the mirror, such that the driver's safety-needed vision of the trailer's rear portion and rear wheels is viewable through the mirror; thus the driver's vision during a turn is permitted and provided by the mirror to be that of maximal safety.