the weight of the arm holds the ball into its oil dampened socket and the string is just used to keep the arm aligned from side to side so it doesnt just fall over.
I thought the string hangs the arm and the ball is inside the oil well but not touching the bottom. Instead of using a magnet, like Schroder, to stabilize the arm from swinging all over the place, the designer use an oil bath to damp unwanted movement. I believe this is the same seller who infringed the Schroder patent and Frank took action against it and now he came up with a different design. Instead of magnet, now it's oil. Very similar concept to the WTA.
Your idea would work too but is closer to a classic unipivot design with the assist of a string for stability.
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