Editing Dark Heresy Second Edition (section)

====Aptitudes====
Aptitudes make things cheaper.  Characteristics, Skills, and Talents have aptitudes; for every aptitude the character shares with them, the character spends less experience.  Characteristics all have two aptitudes; most Skills and Talents have two, but some only have one, where the other aptitude is "General", which everyone has, so no-one pays the aptitudeless cost; conversely, there are rare cases (notably some Inquisitor talents) which only possess one aptitude, period, so no-one pays the cost for matching twice.

To better understand the Aptitudes, here are the Aptitudes and how they map to Characteristics and Skills.

{| class="wikitable sortable"  style="margin-left: auto; margin-right: auto;"
|+ Aptitudes
! Name !! Characteristics !! Skills
|-
| Agility || Agility ||
*Acrobatics
*Dodge
*Operate (X)
*Sleight of Hand
*Stealth
|-
| Ballistic Skill || Ballistic Skill || -
|-
| Defence || Toughness ||
*Dodge
*Parry
|-
| Fellowship || Fellowship ||
*Charm
*Command
*Deceive
*Inquiry
|-
| Fieldcraft || Perception ||
*Awareness
*Medicae
*Navigate (X)
*Operate (X)
*Stealth
*Survival
|-
| Finesse || 
*Ballistic Skill
*Agility
| -
|-
| General || - ||
*Acrobatics
*Athletics
*Common Lore (X)
*Linguistics (X)
*Scrutiny
*Trade (X)
|-
| Intelligence || Intelligence ||
*Commerce
*Common Lore (X)
*Forbidden Lore (X)
*Linguistics (X)
*Logic (X)
*Medicae
*Navigate (X)
*Scholastic Lore (X)
*Security
*Tech-Use
*Trade (X)
|-
| Knowledge || Intelligence || 
*Commerce
*Forbidden Lore
*Logic
*Scholastic Lore
*Sleight of Hand
|-
| Leadership || - || Command
|-
| Offence || 
*Weapon Skill
*Strength
| -
|-
| Perception || Perception ||
*Awareness
*Psyniscience
*Scrutiny
*Survival
|-
| Psyker || Willpower || Psyniscience
|-
| Social || Fellowship || 
*Charm
*Deceive
*Inquiry
*Interrogation
*Intimidate
|-
| Strength || Strength ||
*Athletics
*Intimidate
|-
| Tech || - ||
*Security
*Tech-Use
|-
| Toughness || Toughness || -
|-
| Weapon Skill || Weapon Skill || Parry
|-
| Willpower || Willpower || Interrogation
|}

*So, for example, the Assassin role can provide the Agility, Ballistic Skill (if chosen), Fieldcraft, Finesse, and Perception aptitudes.
**This provides a double match for:
***Ballistic Skill
***Agility
***Perception
***Acrobatics
***Awareness
***Operate (X)
***Stealth
***Survival
**And a single match for:
***Dodge (Defence would pick up a second match)
***Sleight of Hand (Knowledge would pick up a second match)
***Medicae and Navigate (Intelligence would pick up a second match)
***Psyniscience (Psyker would pick up a second match, but this would be very difficult to do)
*And, of course, talents also have aptitude matching.

=====Characteristics=====
Characteristics gain 5 each time they are upgraded, up to a maximum of 5 times (+25).

The first rank if you have two aptitudes is straightforward; its cost is 100 experience.  For every other combination of rank and aptitude, the formula is quite strange:

Characteristic Increase Cost = 250 * (1 + rank + floor(rank/(4+aptitudes/2)) + 3*floor(rank/(5+aptitudes)) - aptitudes)

=====Skills and Talents=====
Skills gain 20 the first time they are upgraded, followed by +10 each additional time, up to a maximum of 4 times total (+30).  

Skill Cost =  100*rank*(3-aptitudes) in experience.

Talents have a fixed cost - the ones that you can take multiple times cost the same every time.  Instead, their cost depends on both their "Tier" (1-3) and aptitudes; their cost is the same as a skill rank one step above the talent's tier:

Talent Cost = 100*(tier+1)*(3-aptitudes) in experience.