I got the same situation with my Polestar tonearm. Here is my method to find the center point:
1. Put a piece of paper tape over the cap of the tonearm where the center is
2. Replace the center pin of the Dr. Feckert by a piece of lead taken from a pencil.
3. Locate the pencil lead on top of the paper tape about 5mm from an estimated center. Let the lead touch the paper tape.
4. Rotate the tonearm cap bay moving the headshell. The pencil lead will draw an arc on the paper tape.
5. The center of the arc is also the center of the tonearm pivot point.