The ARC modes of The Z Factor Perfect Putting Machine teach a putting stroke that follows an arced or curved path. The putter will swing inside the target line on the backstroke, swing back to square at impact and then back inside the target line on the follow through. Inside the target line means the putter will be swinging in toward the golfer during the back stroke and follow through.
These ARC paths (FIVE to choose from) follow swing planes that are at an angle relative to the ground. The curve the putter follows is actually in the shape of an ellipse. The ARC stroke feels very different than the STS stroke and feels more natural to most golfers.
The swing plane can be changed for golfers of different specifications. There are FIVE ARC swing planes/paths available. You can easily change the plane by changing the position of the color-coded spacers - no tools are needed.
While practicing in the Z Factor ARC modes, the face of the putter will open relative to the target line during the backstroke. However, the putter face will still be square to the curved path along which it is traveling. In the follow through the face of the putter will also remain square to the curved path, but will close relative to the target line.
Many teaching professionals believe this opening and closing of the putter is natural and reflects the actual golf swing on a smaller scale.
SQUARE TO SQUARE
The STS mode keeps the putter face square to the target line throughout the stroke. Face angle at impact is the greatest determining factor in getting a putt started on the target line. Keeping the face square to the target line throughout the stroke drastically improves the chances it will be square at impact.