P. 25 - Characteristic BOnuses
"A Characteristic Bonus equals the tens digit of the Characteristic score."
P. 136 Unnatural Characteristic
"select a Characteristic, and double its bonus."
P. 119 Frenzy
"+10 bonus to… [Characteristics]"
P. 161 Enhanced Strength
"Increase the Battle-Brother's Strength by +20. The effect on SB is calculated after the Unnatual Strength multiplier."
P. 202 The Core Mechanic
"-Determine the Skill or Characteristic to test…-Add or subtract any relevant modifiers."
Alright. PCs have Characteristics. Characteristics are measured as being 0-100 (p. 25). The 10's digit of a PC's characteristic is its associated "bonus." Unnatural Trait doubles the Characteristic's bonus.
It is important to distinguish here that it does not multiply the Characteristic itself to determine this bonus. It just takes the flat number, and doubles it. E.g. with a x2 Unnatural Characteristic 3 goes to 6, 4 goes to 8. It is unfortunate that the rules don't provide a base example of a characteristic like "46" having an Unnatural Trait bonus of 8 over 9.
Shows characters with a base Characteristic of 49, and an Unnatural bonus of 8.
Next, let us consider the effects of bonuses and other modifiers to a characteristic outside of the standard +5 Characteristic Advances.
As referenced above, there are two distinctly different ways a stat can be increased:
-A bonus (the most common)
A bonus is applied on top of the characteristic, at the point a relevent test is made, and is not a part of the Characteristic for the puspose of Unnatural Traits. In other words, the Unnatural Characteristic trait is applied at the point of the first step on the Core Mechanic(p. 202), while the majority of effects add in at the second step. An increase is added directly to the characteristic at all times.
Power Armour is a distinctly different modifier, but it specifically states it does not multiply.