I feel like the answers so far are going to make crit very confusing.
The only stats in the game that have base values are things like health, health regen, mana, mana regen, speed stats and critical strike chance.
Stats can be flat like health or percentage based like resistances.
Affixes come in 3 varieties, added, increased and more.
- +10 health is an added stat
- 10% increased health is an increased stat
- 10% more health is a more stat
If you have 100 base health and the 3 stats above, you would have (100 + 10) * (1+0.1) * (1+0.1)=133.1
The same works for percentage based stats. It's just not always obvious that when you see a stat that says +100% increased critical strike chance will only actually give you 5% additional chance to critical hit over base because 0.05 * (1+1) = 0.1 or 10%.