How does one calculate unnatural strength for Space Marines in Power Armor? The power armor grants +20 Strength so do you add this when calculating unnatural strength? Or is it like Death Watch in which the armor doesn't apply to the Unnatural Strength?

Armour doesn't apply to Unnatural Strength.

However, it doesn't really matter, since Black Crusade doesn't use multipliers for Unnatural Characteristics, it's additive instead - it's all explained in the rulebook.

MILLANDSON said:

I know it's additive, however I think I explained it wrong. My question would be if you have Strength of 44 (8) and with Armor it's 64 is it (8) or (10)?

Never mind! Apparently you do add it, as with the Space Marine stat block. My bad.