Armor Class Question

[Deleted]

Hey everyone just have a quick question here.

I've started on my role playing journey at the close of 2nd ed Ad&d, but spent most of my time playing 3rd. After getting tired of those to an extent I began investigating the older editions and the newer clones and really liked what I saw, however as i began reading these forums I see that some people have very strong opinions concerning Desending vs Assending Armor Class.

As i have found in time reading some of these forums this is near and dear to peoples hearts. I do not wish to start a flame war here, I just don't understand and am wondering if i'm missing anything. As far as I can tell they are equivalent.

While I have never had any real trouble understanding THAC0 and such, I am curious what advantages does Desending AC provide of Assending AC?


Thanks everyone for taking the time to respond.
--Griz--

[Random]

Descending AC is traditional, and allows for greater immediate compatibility when sharing materials with other players (well, players playing these same old games) as well as when using old publications. Single digits also take up less space on a paper, making for a (admittedly very slightly) shorter stat block for monsters or NPCs. Descending AC is also easier to use IMO when concocting armor-related house rules (for example, perhaps a PC hurled into a raging current must roll under his AC on 1d8 or else drown).

Last but not least (habits are powerful), many of us are so used to the descending ACs that we have a really good feel for them, and actually have to stop and ponder a moment (or do a quick calculation) to get a feel for how tough AC 17 is, for example.

And as a side note, THAC0 is a ridiculous concept. Descending AC breaks down into an even simpler formula*. That, or you could use those big charts.

*20 - (d20 + modifiers) <= AC will hit.

[chgowiz]

At the end of the day, it's a personal preference. I can play with either (and do play with both) but I remain consistent in a game/campaign - either one or the other.

[philotomy]

I prefer descending, but it's not really that big a deal, to me.

[blissinfinite]

I've used descending AC up until a couple of weeks ago. I just switched to ascending AC (Swords & Wizardry). I got tired of looking up on the charts to hit. Really either one is fine. I think AAC has helped make the game move a bit faster faster (for me anyway) but everyone is still low level. I'll see how things go once higher levels are reached.

[verhaden]

Using descending AC using Delta's Target 20 system, though I'm using the smoothed base modifiers from Philotomy's website instead.

I usually don't even have to think about it.

[EdOWar]

Personally, I've always preferred ascending AC, even house ruling it before 3e came out with it. It just seemed more intuitive to me, and a little easier to use. However, I think descending AC using the Target 20 system would also work nearly as easily.

[Finarvyn]

A good question. Also, we don't have many "flame wars" here because we're just better than most of the other boards.

Others have answered this pretty well, so I'll just toss in a few things and keep moving. Going back to the 1970's I thought descending AC was just strange so I house ruled it into ascending and have pretty much always played it that way. It is all about preference, since many of my friends preferred the book version, and our group would simply hop back and forth depending upon who was the DM at the time.

The game started off with combat charts, and really we’ve been trying to improve on those for 35 years. THAC0 was an attempt to do just that, by making a calculation out of the charts. When I first heard about THAC0 I was really confused, because my own logic told me that comparing anything to AC 0 (which is better than plate&shield) was kind of wacky. In many ways I prefer the 3E approach, which compares everything to a person without any armor at all. Of course, this works better in an ascending format and I suspect that THAC0 makes more sense if AC is descending. So, my AD&D buddies who never switched to ascending AC loved THAC0 and I found it confusing. Swords & Wizardry originally included both versions on their charts. (I’m not sure if it’s still written that way or not, but it does make conversion easy.)

It’s kind of like taking those big nasty percentile charts in Basic Role Playing (CoC, RQ, etc) and saying “well, let’s make a formula out of it and then divide everything by 5 since they are all multiples of 5 anyway” and suddenly those combat systems look a lot more like D&D. Same thing for the James Bond RPG and many other percentile-based games.

A bit off target of the original post, but the key is that you can do it either way and nobody will get too angry at you for it.

[waysoftheearth]

I used descending AC until 3E appeared, then switch over to ascending AC. At the time I thought it was a great innovation. But in the last few years (upon discovering the retro- movement) I have switched back to descending AC, and now I think that descending AC is better suited to pencil and paper table top gaming. That's only my opinion, but I suspect it is because the numbers are smaller, and so the maths is simpler/quicker.

One difference that people haven't mentioned above (or which I missed) is that in the descending system AC 0 is something of a natural "boundary" -- anything less than AC 0 is phenomenal protection. I have heard of some refs requiring magical weapons to hit any negative AC. Whereas in the ascending AC system AC 21 is slightly better than AC 20, but otherwise unremarkable.

I believe this makes the descending AC system a better fit for a games which require a limited range of ACs (between 9 or 10 and 0, say), while ascending AC is a better fit for an unbounded range of ACs (from 10 to infinity).

If you prefer a game with lots of modifiers which stack together (resulting in, say, +21 to attack rolls), then you probably need an unbounded range of ACs. If you prefer a game with smaller modifiers (resulting in, say, +6 to attack rolls), then a smaller range of ACs will likely be enough.

Feb 23, 2010 5:54:48 GMT -6 Random said:

*20 - (d20 + modifiers) <= AC will hit.

I use a slight variation of Random's formula which requires only addition:

d20 + modifiers + opponent's AC >= 20 hit!

d20 + modifiers + opponent's AC < 20 miss


Another "neat" little thing that works well with the descending AC system is that you can compare d20 + AC to various numbers for all kinds of rolls (like swimming, climbing, sneaking and so on) where being encumbered by armour is disadvantageous. Thus you don't need to deal with separate "skill check" modifiers due to armour.

[Random]

waysoftheearth, that's hardly a variation; it's really the exact same formula, just subtracting (d20 + mods) from each side of the inequality and then writing it backwards.

I prefer it written the former way, as I don't like players knowing their opponents' AC values. You never know who has magical protection or is extra dexterous or whatever.

[tavis]

Feb 23, 2010 16:10:23 GMT -6 waysoftheearth said:

II have heard of some refs requiring magical weapons to hit any negative AC.

Some of those refs were emulating Dave Arneson, although like all things in RPGs it was probably also independently invented many times by separate groups.

[Deleted]

Thanks for all the reply's all!

Well i am glad that cooler heads are the majority around here considering what I have read on other forums.

I myself have always liked AAC personally. Just seems more intuitive to me, but I can see where DAC came from and why it was used.

I just dont understand how such strong feeling can emerge over something so seemingly trivial as putting both on the stat block and letting the group decide and some such.

[waysoftheearth]

Feb 23, 2010 18:21:49 GMT -6 Random said:

waysoftheearth, that's hardly a variation; it's really the exact same formula, just subtracting (d20 + mods) from each side of the inequality and then writing it backwards.

I agree, it's the same thing just written differently so that only addition is required. I don't know why, but my brain seems to do small number addition without concious thought, while subtraction requires a moment of concentration.

Feb 23, 2010 18:21:49 GMT -6 Random said:

I prefer it written the former way, as I don't like players knowing their opponents' AC values. You never know who has magical protection or is extra dexterous or whatever.

I also agree it is a "good thing" to keep absolute information from the players. I have my players tell me their die result and the modifier (if any) they have due to PC level and stats. I do the rest of the sums and tell them if it's a hit or a miss. The players never need to know their opponent's AC.

Of course they can try to deduce their opponents' ACs during combats, but that's all part of the fun

It's actually very interesting to observe how several "high rolls that still miss" can sway the players' strategy during a combat. It can be very much like a subversive player morale effect...

[Random]

That makes sense.
I do math for a living currently, so I guess subtraction doesn't phase me.

[fitz]

I much prefer AAC and thought it was one of the real improvements of 3e; I use it exclusively in my S&W campaigns.

I suspect my preference is because I find it easier to add numbers than subtract them -- I don't know why.

[kenmeister]

Feb 23, 2010 16:10:23 GMT -6 waysoftheearth said:

One difference that people haven't mentioned above (or which I missed) is that in the descending system AC 0 is something of a natural "boundary" -- anything less than AC 0 is phenomenal protection. I have heard of some refs requiring magical weapons to hit any negative AC. Whereas in the ascending AC system AC 21 is slightly better than AC 20, but otherwise unremarkable.

Yup, I picked up a good rule on the very last page of the 2E supplement Player's Combat & Tactics which says to treat the negative portion of a monster's armor class as its magic bonus. In other words, a monster with armor class -3 has the same benefit as a character wearing +3 magical armor with regards to saving throws.

[coffee]

I don't have to subtract -- I use descending AC, look at the table, and know what number I need to roll to hit. Looking at tables holds no especial fears for me.

(For the record, I was never a fan of THAC0, anyway.)

But in my case, it's just burned into my memory. I'm in an AD&D game for the first time in at least 20 years, but when someone asks the DM "I have leather armor and a shield, what armor class is that?" I usually answer (seven!) before the DM even realizes someone's asking him anything (he's still finishing up with the person he had already been talking to).

(Of course, then I have to look it up to make sure I'm right, but so far I have been.)

[jblittlefield]

I figured out ascending AC around 1979 or so... I hate charts and tables.

[bluskreem]

I prefer descending because there is something visceral about consulting a chart to see the results of combat.

Awhile back Snorri suggested a Stealth subsystem that had 1d20 vs AC + Dex Mod + level, which works wonders in my Carcosa games (there is no thief or halfling in OD&D)

[ragnorakk]

Feb 23, 2010 19:12:51 GMT -6 @grizaptimus said:

I just dont understand how such strong feeling can emerge over something so seemingly trivial as putting both on the stat block and letting the group decide and some such.

I think that's mostly an 'internet thing': people flaming about whatever because it's easier to get away with... in the end, the maths are the same, so I think it comes down to personal preference/history. I prefer descending, but I can't really back up why with any kind of logic - it's just the way I am used to it - though the observation above that it does seem to fit well with a limited range of AC is interesting. Obviously there's nothing stopping someone from imposing an upper boundary on ascending AC, but this way the work is done front-loaded!

[waysoftheearth]

I recall reading a nice summary about how the arithmetic of AC works in people's heads a while back...

Ah yes, it was on Delta's blog here .

Essentially, Delta discusses how smaller integer addition is faster in people's heads, and hence the system of smaller numbered (descending) ACs is actually easier and quicker to work with in play than larger (ascending) ACs.

Mathematicians and super-geniuses, may differ in this regard...

I was also happy to find that the method I've arrived at is pretty much the same as the one that Delta found to be optimal ;D

[Random]

No, mathematicians prefer descending AC as well.

[dwayanu]

While I have never had any real trouble understanding THAC0 and such, I am curious what advantages does Desending AC provide of Assending AC?

1.That's how hundreds of monsters are written up -- over 350 in the 1977 Monster Manual alone .

2. That's how the Armor Classes are listed in the rules, on the tables of rolls to hit.

[irdaranger]

May 2, 2010 17:45:51 GMT -6 dwayanu said:

While I have never had any real trouble understanding THAC0 and such, I am curious what advantages does Desending AC provide of Assending AC?

1.That's how hundreds of monsters are written up -- over 350 in the 1977 Monster Manual alone .

2. That's how the Armor Classes are listed in the rules, on the tables of rolls to hit.

3. That's how all the best modules have monsters and NPCs noted.

4. It's actually faster to calculate in your head, once you know your to-hit modifier.

#4 seems counterintuitive, but here's the algorithm:

d20 + to-hit + mods + AC ≥ 20 == Hit.

Note that you don't have to even finish the calculation most times, because once you hit 20 you stop. Natural 20? Done. 17 + 4 (to-hit)? Done. Etc. You only ask for the AC (or ask the DM if you hit, if he wants to keep the AC under his hat) if [d20 + to-hit + mods] is still less than 20.

You calculate your to-hit for each weapon by reading the ThAC0 line off your class's attack matrix, and then adjusting for STR or DEX, magic bonus, weapon mastery (if you use rules like that), etc. This number should not change except when you level or get a weapon with a higher magic attack bonus.

The mods are situational though, such as a bonus for attacking from higher ground, or Weapons vs. AC (if you used that rule from AD&D - not necessarily applicable here).

[dwayanu]

irdaranger says: "d20 + to-hit + mods + AC ≥ 20 == Hit. ... You calculate your to-hit ..."

Yeah, that step is one you did not explain clearly. Suffice to say that it's "half a dozen of one" versus the "six of another" of calculating ascending AC.

YMMV as to which is faster.

Try this:

A first-level character hits on 11 or less. That is, for instance, 28 less the 17 needed to hit AC 2 (per the "Men Attacking" matrix in M&M). A +2 to hit makes that 13 or less.

Only when the attack factor goes over 20 do we get into arithmetic on the roll. A top-level fighter (hitting AC 2 on 5+ per the matrix) has a base factor of 23, which means +3 on the roll.

Defense factor is simply 9 less AC: from 0 for nothing to 7 for plate and shield. Penalties to the attacker can be added to the DF instead of subtracted from the AF.

Roll over DF, but not over AF, to score a hit.

So, a combatant with AF 16 taking a whack at one with DF 5 hits on a roll of 6-16 and misses on any other. There's no math, other than recognizing which numbers are simply higher or lower than which others.

An 11+ HD monster (AF 21) attacking a guy in excellent magic armor (AC -1 = DF 10) adds 1 to the roll and hits on a final 11+ (or 10+ with the +1 factored in).

The idea, as with such other AC systems as Palladium's or WotC's, or armor stopping damage as in RuneQuest or in the Dawn of Emperors D&D Gazetteer, is of course to switch over systematically. Note the numbers once in your monster manuals and so on, rather than having repeatedly to convert.