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Grubby just came up with this question on Twitter

SC2 math heads: what's better for a Stalker, 1 armor 1 shield or 2 armor? I heard 2 armor is better before but I don't know why necessarily.

I'm curious if we could answer this with our communities math-skills :)

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That's dependent on the state of the game, assuming early game pre-ghost vs terran and no emps, it's pretty much equal. After EMP though, armor is going to be better because a well placed EMP will wipe out the shield. It also depends on what you're fighting as well, it's a really broad question. – Sorean Oct 17 '12 at 6:27
up vote 6 down vote accepted

At first, let us look at the basic numbers:


  • 80 Shield
  • 80 Health
  • 1 Armor

Every Armor upgrade gives them +1 additional armor and every shield upgrade +1 shield armor. But how does Armor work exactly? Liquidpedia tells us:

Damage by incoming attacks is reduced by the amount of armor: every point of armor reduces the damage received by one point. Units attacking in volleys, like the Zealot and the Thor, have the target's armor applied to each of their attacks. [...] Protoss Plasma Shields use a separate armor value for computing damage to the shields, starting at 0 for all Protoss units and buildings and growing by 1 for every Shields Upgrades.

During early stages of the game it is pretty easy to micro away Stalkers that took too much damage to their shields and prevent damage to their health. Shield upgrades would have an advantage there. But as we are talking about 2 upgrades it is not early game anymore and army sizes are getting bigger.

Considering Stalkers amount of Health and Shield is the same, damage reduction with both upgrade combinations is equal. That is why we want to look at how many hits a Stalker can take from opposing units. The spreadsheet indicates that +2 Armor has a slight advantage in general.

Additionally to that you have to be beware of EMP in PvT: If the opponent has Ghosts, Shield upgrades may be worth much less.

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If they are almost the same you might get a benefit from going +1 Shields first to get the Micro benefit and later add +1 Armor. But your conclusion is better if you just look at the numbers after the two upgrades. – ayckoster Oct 17 '12 at 12:28

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