I can't answer that question with any relation to Fallout or Fallout New Vegas. I have played Fallout but not completed it and when I did play it I didn't take too much notice of it's systems (because it didn't really require me to). Haven't played F:NV.
The P:E armor system has undergone a few revisions and I *think* is currently on it's 3rd revision which hasn't changed for a while.
This was
the last official armor update.
In the Update 51 forum thread over at obsidian I asked a question about armor and Josh replied
The armor system hasn't changed since the last revision a while back. The system currently uses a single DT for a suit of armor with additional modifiers applied for things it is better or worse at. E.g. ordinary mail has 12 DT but it is 40% worse against crushing attacks.
This description is different from the last Kickstarter update about it but he may have been talking about a Formspring or SA discussion, I cannot remember.
Then there is also this SA forum post
Procs have their own voodoo math for calculating damage vs. DT. Procs are always a percentage of the weapon damage, so the proc damage is compared to the same percentage of DT, modified (if necessary) by special damage type resistances.
N.B.: While we will typically show damage and armor values in integers, we will actually track them as floats.
E.g. if you hit someone with a sabre that does +20% Shock damage, you would calculate the base (Slash) damage -- let's say it's 20 -- then the Shock damage, 4. The target is wearing armor that has 8 DT, no special modifier for Slash damage. It takes 12 damage from the sabre itself. The armor has -30% Shock DT, so that goes down to 5.6 DT, which is then reduced to 20% its normal value (because the proc is 20%), or 1.12 DT. The target takes an additional 2.88 damage from Shock, for a total of 14.88.
So my current understanding of the armor system is as follows:
The game has DT which is essentially DR, it is no longer some weird mathematical system (which IMO did seem rather cool). It is very simple.
Let's say you're wearing Hide Armor which has 8 DT and no special modifier for Slashing damage, and you are attacked by a Sabre wielder for 20 damage. Your armor reduces this value to 12 damage.
If you're wearing a Mail shirt (or Chain Mail or Hauberk depending on P:E's level of nomenclature) with DT 12 and you get hit with a Mace for 16 damage, the effective DT against Crushing is 12 - 40% (4.8) = 7.2 so you take 8.8 damage from the Mace.
It's interesting because Josh does not mention minimum DT which was a value in the first armor system's table where a weapon would always do some damage. So there may be some minimum value that gets through armor that he just has not mentioned in the last two posts. Probably a good question to ask him about actually.