The mechanism is hidden in the base. The pics will not make it clear how it works. A video would be better. There are two horizontal pivots in the base that articulate. There is also a guide rail hidden in the base that guides the arm in a straight line across the record. From what I understand there is a magnet that helps with that process. The bearings are also very low friction and because of that there is no excessive horizontal mass unlike most linear tracking arms. They also claim no skating force is generated.
No string involved in this design.
No string involved in this design.

