Len, Steve.... a watts link is a set of two bars attached to a pivot point
mounted on the center section of the rear end... looks about like this...
the bars are longer then I can draw here.
The intent of the arrangement is to allow the center pivot to move up and
down but maintain the ability of the upper and lower bars to absorb the
deflection based on the center pivot point... that way the rear end
maintains it's alinement throughout it's range of travel.
With the Stock pan hard rod there is actually a moment that tends to drive
the rear end one way or the other.... based on it's altitude....
Hope that makes some sense...