Basic Motion Question
 

12-5-1 Basic Motion lists Rhythm as a component (in fact it's listed as a component for an abbreviated version of the Basic Motion). I'm not sure I understand why it's listed at all. If Rhythm is "holding both Lever Assemblies to the same basic RPM throughout the stroke...", why would we be concerned about rhythm at this stage when #3 accumulator is zero? It seems like it should first be introduced with the Acquired Motion. What am I missing here?

The simple answer is that in every stroke no matter its length, there is a hinge action and even with zero #3 accumulator, you can still bend your left wrist.

Rhythm Ruin
 

Each of the three Hinge Actions (Horizontal, Vertical and Angled) can be executed with Zero #3 Accumulator. Normally, each Hinge Action produces a different amount of Clubhead Travel through Impact to the end of the Follow-Through (Both Arms Straight position). But with Zero #3 Accumulator, each has Angled Hinge Action Rhythm (Clubhead Travel to the end of the Follow-Through,i.e., the Both Arms Straight position.

However, as The Slinger has said, it is quite possible to Bend the Left Wrist when using Zero #3 Accumulator. As is the case with #3 Accumulator, this puts the Clubshaft out-of-line with the Left Arm, disrupts the Clubhead Orbit and thus destroys Rhythm.