Spinning Rock

This 30-foot tall structure appears to be a set of 8 disks set on top of one another. The total diameter of the structure is 25 feet.

The top disk clearly spins clockwise at a constant rate, taking somewhere between 4-5 minutes to circle completely. After each revolution, the next lower disk moves a small amount.

None of the other disks has been observed to move; instead they are covered with symbols. (Note that the top two disks have no symbols at all.) A small (0.1 mm) red line has been observed to run along all 8 disks; never moving despite the fact that the top disks are spinning. The third, fourth, and fifth disks from the top all have circles carved into them, each with various amounts of that circle carved out of them. The same eight configurations exist on all three of these, although the "bottom" of these has sets of 3 identical symbols. All, however, exhibit the same order of symbols:

1. Full circle (only oultine carved)
2. Right "crescent" removed
3. Right half removed,
4. All but left "crescent" removed
5. Entire circle removed
6. All but right "crescent" removed
7. Left half removed
8. Left "crescent" removed

From top to bottom, the red line passes through the 4th circle of the third disk; the sixth circle of the fourth disk, and the eighth circle of the fifth disk (middle of three such symbols).

The remaining symbols are unknown to the group and all different on each disk. The sixth disk from the top has 13 symbols; the seventh disk has 12 symbols, and the bottom disk has five. The red line aligns with one symbol from each disk.