Arctic armour and armour calculation

GGG did a fair job of using very specific wording for their mechanics, and a good lot of information can be gleaned from said wording, if you know what to look for:


Armour and Endurance Charges (among others) specifically use the words 'Damage Reduction'. Arctic Armour is instead a modifier to 'Damage Taken from Hits'.
From the difference in wording alone, we can tell that it's a separate mechanic from Armour. The order of these mechanics could be intuited either way, but Damage Reduction comes first.
(Damage Taken has to be calculated before it can be modified, is the train of thought)

Now let's take a look at other modifiers that do use similar wording: Fortify, and Abyssus.
The Fortify buff grants 20% Reduced Damage Taken from Hits.
Abyssus grants 40-50% Increased Damage Taken.

Increased and Reduced type modifiers are always additive with eachother, whereas Less and More are always multiplicative. From this we can deduce that Fort and Abyssus would be added together (if both are applicable), and Arctic Armour is instead a separate multiplier.

Additionally, both Fort and AA specify "from Hits": they do not apply to Damage over Time. Abyssus does not specify, and thus will apply to Damage over Time.


I personally found it super useful to learn the "language", it makes understanding different and new mechanics easier :) Considering the time I have spent here, it was well worth the small investment of time back then, haha.