Editing Dark Heresy Second Edition (section)

=== Basics ===
A quick explanation of what the choices do, first.
====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.

====Characteristic Bonuses and Penalties====
By default, the 10 characteristics are all 20 + 2d10, so 22-40, with an average of 31 (most GMs will let you generate your 10 scores, then allocate them, but RAW, you generate them one at a time, and live with what you are given).  You can, instead, use point buy, which gives you 25 in every characteristic and then 60 discretionary to distribute, with a maximum of 40; if you distribute your points evenly, you will have exactly 31 in every characteristic.

A characteristic bonus works differently for each model.  If you are rolling, a characteristic with a bonus is 20 + 3d10 keep the two highest, which means your two characteristics with a bonus become, on average, 33.475 rather than 31, or a net bonus of +2.475 to each (4.95 total).  By contrast, the one with a penalty is 20 + 3d10 keep the two lowest, which drops it by 2.475 on average (typically to 28.525).  

If you are using point buy, instead each of your bonuses adds 5 to the relevant characteristic and your penalty subtracts 5 (giving you the only legal way to start with a characteristic at 20).
====Fate Points and Wounds====
For both of these, your starting number is also the maximum you regenerate to - if you start with 4 Fate Points, the most you can have is 4, and if you start with 2, the most you can have is 2 (Fate Points come back every session, but your maximum can come up if you encounter a mechanic for getting more mid-session).  Same with Wounds - whatever you start with is how many you can be healed up to.

You gain more maximum wounds later with the Sound Constitution talent (300 experience, 200 with the Toughness aptitude, per buy, maximum buys Toughness Bonus + 1); you only gain maximum Fate Points as the GM's discretion, and the rulebook has a stern warning that this should be given out very rarely for monumental accomplishments or selfless sacrifices. However, you do get a chance to start with one extra maximium Fate Point via the Emperor's Blessing; roll a d10 and if it's greater than or equal to the result designated by your homeworld you'll get the bonus.