Alright, I am in a discussion with a player, I went to see if they fixed this in Only War, but they didn't, and it's just confusing as hell. The Table on Psychic Strength (BC Core, pg. 206) specifically says "+10 to all rolls on the Psychic Phenomena Table, decrease Psy Rating by 1 per power" .

Now, I always took this as meaning that for every Sustained power, if you'd get Phenomena, you'd add +10 to the result, and you'd reduce your total effective Psy Rating by 1 when using powers. So if you before had a Psy Rating of 5, you'd now have 4, effectively stopping people from Sustaining more powers than their Psy Rating.

However, the Text says that there's no penalty at all for sustaining a single power, except for the Sustain Requirement, which is a power-by-power case rule clarifying what kind of action you must use to Sustain a power.

It then goes on to say that if you are Sustaining more than one, you add +10 to Psychic Phenomena for every power being sustained beyond the first , and lower the Psy Rating of the powers being sustained by 1 for every power (so, if you are sustaining 2, you lower the Psy Rating of both by 2).

Even if we assume that I have been wrong about the way to read the reduction of Psy Rating in the Table (that it meant to reduce the Power(s) being Sustained by 1, which makes no sense if it's just 1 power), the text and table does not match up. One of them has to be wrong in one way or another, they cannot both be true.

This isn't just in Black Crusade. I checked Only War and the Erratas, but it doesn't clear up the issue.

For reference, these are the texts:

Table:

+10 to all rolls on the Psychic Phenomena Table, decrease Psy Rating by 1 per power.

Text:

Some psychic powers can be sustained for a prolonged period of time, as noted in their description. A psyker may sustain such powers without the need to make further rolls, taking only a small amount of effort to sustain a single power. However, attempting to maintain multiple powers at once becomes increasingly taxing, dividing the psyker’s attention between several simultaneous effects and requiring ever-greater amounts of concentration.

Any power that can be sustained has a listed Action which defines how much effort the power requires to sustain — for example, a power with a Sustain Requirement of Half Action requires a Half Action each turn to sustain its effects. If the psyker is only attempting to sustain a single power, this is enough to maintain the effects. Any power that does not have the required action spent to sustain it ends at the end of the psyker’s turn.

Sustaining multiple powers is more diffi cult and more tiring. Any character attempting to sustain two or more powers at once must spend the longest action from the Sustain Requirements of all the powers being sustained, and reduces the effective Psy Rating for each power by the number of powers being sustained. More perilous still, the amount of energy the psyker is attempting to wield becomes unstable, swiftly going out of control at the most minor slip of concentration. Should the psyker cause Psychic Phenomena while sustaining more than one power, then he should add +10 to the result rolled on Table 6–2: Psychic Phenomena for every power after the first being sustained.

For now, I have informed the player that we're taking the most lenient approach I can take in regards to this, arguing that both parts of the Table only applies to powers beyond the first, essentially taking the least punitive effect from the Table and the least punitive effect from the Text in an effort to reconcile the two.

So I will ask him to reduce all Sustained Powers by a PR of 1, and add +10 to Psychic Phenomenas, but only for every Psychic Power that is Sustained beyond the 1st.

Any ideas on how to interpret this? For now, I think my solution makes the most sense and it's rather neat, but I don't think it's entirely correct.

This looks to have been an editing error that snuck into Black Crusade and was never fixed when Only War was printed. Dark Heresy used an entirely different system to determine whether powers went off (ugh), Rogue Trader used a similar table but explicitly noted that the malus was for "Sustaining Multiple Powers", and Deathwatch simply toyed with eliminating the table.

It's times like that I pine for some declaration of rules primacy in case a contradiction occurs. (D&D 3.x did this, but I'll be damned if I go back to that system without kicking and screaming.)

I know, D&D 3.X has the rule that Text trumps Table, but there's no blanket rule for that in WH40kRP. I'm just surprised (although honestly, not really) that this was never catched in an Errata, nor fixed between Black Crusade and Only War.