A real pendulum, hung from your hand
Dowsing pendulums are usually explained badly, which is a shame, because the physics is genuinely satisfying. A weight on a cord has a natural period that depends on the length of the cord and almost nothing else. Drive it at that period, however slightly, and the swing grows. Drive it off that period and it fights you.
Instrument 16 simulates a bob with correct inertia and damping, hung from the top edge of your phone and driven by your accelerometer. Hold the device still and it settles. Hold it as still as you can while asking a question you care about, and it will not settle, because your hand is not still and never was.
The swing you get is your own micro-motion, amplified by resonance and then read back to you as an answer. That is the ideomotor effect again, working through better mechanics.
It is a real pendulum. It is not a real oracle. Both of those are worth knowing before you use it.