To make the movement a-magnetic, they used rubies as rotor ball bearings (like in the compass watch). And for the balance spring they used a new alloy which could not be magnetized. However, the alloy was an issue in terms of accuracy and production and individual testing (and the high number of "fails") led IWC to stop this project quickly. So, the number of "500'000 A/m" models is very limited.
Cheers, HSTE