The Watts linkage can be either “axle mounted” or “chassis mounted”. This refers to the location of the Watts lever pivot axis.

Axle mounted Watts link pivot.

There are five or six chassis mounting points, one for each trailing link, one for each Watts link.
The 3 trailing link configuration has only one top link.

There are five or six axle mounting points, one for each trailing link, and two for the Watts pivot, one of which is reference point to determine the pivot axis.

Chassis mounted Watts link pivot.

There five or six chassis mounting points, one for each trailing link, and two for the Watts pivot, one of which is reference point to determine the pivot axis.
The 3 trailing link configuration has only one top link.

There are five or six chassis mounting points, one for each trailing link, one for each Watts link.