[Lazy_Perfectionist]

Parry is Defense - except not.

First thing to keep in mind is that the unit information displays a summary. You're going to have to click equipment and number for precise details and the actual numbers used in the math. You'll have to hit the manual if you want the precise formulas - it is in there - but I'm leaving it simpler for this post. When you see DRN, just think die roll. That's close enough, though dominions has its own special version.

For melee hit calculations:

If attack + DRN exceeds Defense + DRN + parry, then a hit is generated that rolls against the protection of the body part hit. (See note 1) Think of this as a very skillful attack that slips past the shield and hits their armor.

If attack + DRN exceeds Defense + DRN, but not Defense + DRN + Parry, then a hit is generated that rolls against the protection of the body part + the protection of the shield. Think of this as an attack that is deflected by the opponents shield. Blocking a warhammer with a shield hurts, but not as much as blocking it with your head.

If attack + DRN is less than Defense+DRN, then its a total miss. No protection role is generated. A whiff.

Missile Combat:

Parry only comes into play if a single-target, non-lightning missile comes into play. Think arrows, crossbow bolts, and flame bolts.

If DRN + Six (see note 2) exceeds 2 + DRN + twice the parry value - fatigue penalty, then the arrow hits the target.

If DRN + Six is lower than 2 + DRN + twice the parry value - fatigue penalty, then the arrow is deflected, harming nothing.

When you look at shields you want to consider a few things.

Defense: Most shields carry a defense penalty. This penalty is negated somewhat by the parry value. The unit may get hit more often, but most of those hits will be 'shield hits' and won't get past the extra fifteen protection. The effective result versus other humans is often less damage taken, less 'hits', but versus exceedingly strong giants who're stronger than the shield's protection a shield hit is no longer a good thing.

Parry: Offsets the defense penalty and has a huge affect on missile avoidance. A kite shield is a very effective tool for avoiding missiles. For instance, if I do my math correctly:
a buckler (2 parry) will block about 54% of arrows.
a tower shield (8 parry) will block about 98% of arrows.

Encumbrance: More is bad. How much so depends on the unit. You won't put a tower shield on many mages because it makes spellcasting much more exhausting. Instead, you'll go with something light like a raw hide shield or weightless kite shield. On the other hand, while encumbrance affects melee, it does so on a much lesser scale. That heavy shield will definitely go on your thug if you're facing Man, with their longbowmen.

Protection: It's almost the last thing to consider with a shield. It's only relevant in melee combat, and a highly skilled opponent (fire bless anyone?) rarely gets shield hits, let alone misses, often going straight to the body armor. However, taking that tower shields defense penalty and parry into account, you are getting a net defense gain of seven.

In a battle between two normal (10/10) unshielded humans, 46% of attacks hit, and 54% miss.


In a battle between two normal shielded humans, 70% hit (shield or body), and 30% miss completely. Your actual defense (which affects true misses, has gone down by two. However, your practical defense has gone UP by seven. 92% of attacks will either miss or hit your shield. Only 8% will manage to beat defense+parry, resulting in a strike to your body/head. If I've done my math correctly, when we combine these facts we see that..

Less attacks miss completely (only 30%), but most hits (62%) get the protection of the shield added to the damage calculation (instead of say, 8 protection of just a helmet, they get the 8+28=36 of a shield hit) and only 8% go straight to body part.

Feel free to correct me if I've made mistakes, but please be gentle. It wasn't easy writing this, and it was the first time I've tried to explain this in quite this way.

Note 1: By straight to the body part, I mean a head or body hit, and armor is included in the calculations if worn.

Note 2: DRN + six is a simplification. The real calculation includes how densely packed the target square is, and whether magical projectiles are being used. In most cases, it comes out to six.

I hope this was of help. To answer which is better... I assume you're comparing shields. You need a high parry value to take advantage of shields. Without parry, the protection is useless. However, any parry value six or greater is excellent. After that, you're not choosing between parry values so much as choosing between protection and encumbrance.