First off there are 2 types of skills:
There are 4 levels of skills:
Untrained: You have not purchased any advance for the skill
Trained: You have purchased the advance for the skill
Expert (+10) mastery: You have purchased the 'Skill (+10)' advance for the skill
Master (+20) mastery: You have purchased the 'Skill (+20)' advance for the skill
I guess BC has a third level of mastery?
Finally there is a talent called 'Talented (skill)' which you gives you a +10 to all tests for that skill.
First I'll cover Basic skills
A basic skill is such a simple skill you MAY use the skill even if it is UNTRAINED, but the skill test is at HALF of the skill's characteristic.
You DO NOT halve modifiers when using an UNTRAINED Basic skill, only the associated characteristic.
If a basic skill is TRAINED then it is used normally at FULL characteristic
Second I'll cover Advanced skills
An Advanced skill is pretty complicated, it may require extensive training or specific knowledge for instance, you MAY NOT use an advanced skill if it is UNTRAINED and any tests you have to take with an UNTRAINED Advanced skill AUTOMATICALLY FAIL.
Once an Advanced skill becomes TRAINED it functions as a normal skill.
The mastery levels ('Skill (+10)' and 'Skill (+20)') work by INCREASING your characteristic associated with that skill when taking tests for that skill. A character with Agility 20 and Dodge (+10) tests to Dodge on a 30 (not a 20).
Mastery levels ARE NOT bonuses to the skill test. Therefore mastery levels CAN be combined with the bonus cap. If the previous example took a +60 dodge test he would need to roll under a 90 (Dodge characteristic of 30 +60). If mastery levels were bonuses then the character would have to roll under an 80 instead.
You CAN NOT purchase masteries for UNTRAINED Basic skills, so don't worry about that.
The 'Skill (+20)' replaces the 'Skill (+10), they do not add together.
The 'Talented (Skill)' talent provides a +10 MODIFIER to skill rolls made with the skill. This MODIFIER IS combined and limited by the modifier caps. Using the previous example again: The character now has 'Talented (Dodge)'. If he takes a +60 test he will need to roll under 90, NOT 100 as the +10 modifier from talented cannot raise the modifier cap above +60. Although it can negate negative modifiers and improve positive modifiersin the same way normal test modifiers do (the 'talented' +10 bonus will decrease a -20 penalty to a -10 and increase a +50 to +60 for instance).
You can have 'Talented (Skill)' and not have any masteries. But lunike masteries, you CAN have Talented for UNTRAINED Basic skills IF your advance table allows you to purchase it without its associated skill as a prerequisite.
Okey so let me see if I got it right…
Basic Skill Dodge for a starting space marine.
This means that to dodge something he has to roll under his agility (in this case 55) halved down (27).
If that marine picks up the Dodge skill at rank 1 in the general space marine skill chart, he pays 200xp and dodge becomes trained
Trained = He takes dodge tests at full agility (55)
The rest is quite clear, all the bonus derived by the +10/+20/Mastery/Talented
Since I'm here to ask, I'm looking at the Characters sheet for DeathWatch and I see that some skills have been marked down as trained already but the basic skill slot is not checked out.
For example Literacy.
Others instead has both slots marked down, for example Silent Move.
The question is: Do I need to buy the basic skill when on the sheet is already marked the trained that comes with the basic character?