Quote Originally Posted by Haruspex_Pariah View Post
I sure hope this hasn't been answered sometime before but...

How exactly does your average planetary governor know how to tell psykers from non-psykers in a planet's population? And how do the Black Ships know if a world is doing its due diligence to get them?

Would they use a percentage estimate? e.g. each time we visit we expect at least [x]% of your population to be psykers. Or are there witch-seeking tools (that actually work)?

I initially thought that they would wait for an obvious manifestation and then swoop in, but considering what a single untrained psyker can do, that seems dangerous.
I recall in Descent of Angels or one of the other HH Dark Angels books they were discussing that Caliban had an unusually low incidence of Psykers, even compared to other worlds that executed their witches. So that at least implies that the Imperium knows how many psykers to expect from a planetary population even taking into account witch-burnings. But that was pre-heresy so who knows if they've maintained a consistent record to judge individual worlds by.