Armor Class

About

• Armor Class (AC) is displayed in 'score' as well as served by MSDP.
• AC is a negative value. The more negative the better.
• AC is primarily consulted in relation to melee attacks

Historical Basis in D&D

• Armor Class in SMAUG 1.8 is based on older D&D editions that used the "To Hit Armor Class 0" (THAC0) approach.
  • Realms source code has variables for "thac_00" and "thac_32" specially, so while I am sure the exact implementation differs, the premise of the system is likely similar.
  • See: https://dungeonsdragons.fandom.com/wiki/THAC0
• I'm not going to reverse engineer how this works mechanically, the point is it's like D&D so make some assumptions.

Item AC vs. Player AC vs. Affects AC vs. Mob AC

• Item AC:
  • Each item has it's own AC, displayed in 'identify' output as: "Armor class is ## of ##."
    • This number defines how many hits the item can take before it scraps.
    • Repairing the item resets this back to its max.
    • Acid attacks may 'etch' the equipment, reducing its max AC. Not repairable.

• Player AC:
  • The sum of all your Item AC's. Except not really, there's one caveat:
    • The calculation depends on the wearable location of the item. Some are summed, some are negated, some receive a multiplier. (see below)

• Affects AC:
  • Some items also have "Affects AC by -##" as one of their attributes
  • This number is added to your Player AC

• Mob AC:
  • A mob has its own inherent 'naked' AC (think of this as their skin)
  • A mob may be wearing equipment that increases AC (just like players wearing equipment)

Mechanics

• Melee attacks compare Hitroll against AC to determine if a melee attack hits/misses.
  • It is believed that 1 HR of attack equals 10AC of defense. (10 hr vs. 100 ac would be a tie)

I'm not reallllllly going to dig into this. But, let's just make up some ways it might work!

Let's just call HR 'hit' and AC 'defend', and ignore the negative value aspect of AC to make things simple:

Player: 100 hit, 1000 defend
   Mob: 50h hit, 500  defend

If HR to AC is calculated at a 1/10 ratio, then let's just immediately reduce those ac values accordingly:

Player: 100 hit, 100 defend
   Mob:  50 hit,  50 defend 

So, if we hit for "100", we're going to succeed, because the mob can only defend "50" really.

I think in short that's the spirit of things, and it's probably sufficient to leave it there for a rudimentary understanding of how AC/HR work together.

Dodge/Parry Factors

Old Code vs. Current Code

One major caveat here is that it is known that historically, Mob AC was limited to a max -300

Newer SMAUG code can however set Mob AC to the full -1000 value so, things are different now.

Due to the old limitation however many 'old mobs' still use those low values, so player HR had/has to be kept toward low values, or we would nearly always hit.

Additionally, many mobs simply have other 'workarounds' coded to ensure melee damage misses most of the time.

Lowbie Display

Until level 25, a player does not know their exact AC, instead only seeing a brief description based on the value as seen in the table below:

AC	Description
-201 and lower	that of an avatar
-101 to -200	the envy of emperors
-81 to -100	the envy of dukes
-61 to -80	the envy of barons
-41 to -60	the envy of knights
-21 to -40	excellently crafted
-11 to -20	the envy of squires
-1 to -10	well crafted
+9 to 0	moderately crafted
+19 to +10	that of a knave
+39 to +20	scant protection
+54 to +40	of poor quality
+79 to +55	shabby and threadbare
+100 to +80	improper for adventure
+101 and higher	the rags of a beggar

Slot Multiplier

From 'help ac' we are told that where a piece of equipment is worn also impacts its functional Armor Class:

"Items worn on extremities or wielded will not have any effect on the wearer's AC"
"Key locations (Body, Legs, Head) will multiply the item's AC by 2 or 3"

Worn Location	Multiplier	Example Item AC	Example Applied AC
Finger	-	10	10
Neck	-	10	10
Body	x 3	10	30
Head	x 2	10	20
Legs	x 2	10	20
About	x 2	10	20
Waist		10	10
Wrist		10	10
Shield		10	10
Hold		10	10
Weapon	x 0	10	0
Ear	x 0	10	0
Eye		10	10
Back		10	10
Face		10	10
Ankle		10	10