Friday, January 25, 2013

Is the Main OSR Division Descending / Ascending Armor Class?

Is Descending Armor Class the "sacred cow" of the OSR?

Is it the one thing some folks have decided to draw the line at?

I can actually understand the desire to remain "true to the original form" and I personally found the change of the later editions of D&D to Ascending AC as an affront of my personal ideal of what defined D&D.

I started with AD&D 1e. I didn't get a DM's shield for years (and initially refused to cut up my issue of The Dragon to remove and set up the Combat Wheel). The pages of the Combat Charts in my original DMG took a hell of a beating over years of use, all because of the constant need to refer to the Combat Charts.

The thing is, as I've gotten older, I care less about "the purity of the game", which I suspect is where the  line between Descending AC and Ascending AC gets drawn. Ascending or descending, the results are the same but with ascending AC the math is simpler, as there is next to no math. You roll to hit AC. Add your modifiers and you are done. You know if you hit right then and there.

With descending AC, you either refer to the chart OR add your target's AC to your modifiers roll to hit and if the total is 20 or higher you hit. I think that's how you go chartless with descending AC. This would be THAC0, kinda sorta. THAC0 was an attempt to move descending AC away from the combat charts. THAC0 gave you a starting point with some of the math filed off. It certainly helped.

Player's have it simpler in either case, as they can writet down their standard To Hit array on the bottom of their character sheet.

DMs don't have that option.

I'm NOT going to re-gigger my 1e / OSRIC campaign to use ascending AC. In such an attempt lies madness. I am going to spend an hour or two writing the THAC0 for all the creatures in Rappan Athuk's immediate levels, so I can save some damn chart referencing time during game sessions.

I still think ascending AC makes more sense, even if descending AC is more authentic.


  1. Played both way and I much prefer ascending AC. I do have to say that doing THAC0 for years has made me better at doing math in my head than my kids are. However I just decided that the difference between Old School and d20 is the amount of experience you get for slaying an orc. To be honest, I'm kind of blown away by the game impact the difference makes.

  2. It's really not that much effort to change 1e to ascending AC. Just have to re-do the tables once which took me about 30 minutes.

    What I also did was to go to ascending saves (and go from 5 saves to 3 from 3e). That seems to be the real line in OSR - a number of OSR games use ascending AC, but I don't think any use ascending saves (though Blood & Treasure also adopts the 3 save).

  3. I prefer Ascending AC. It's just more intuitive for me. S&W shows it's super easy to convert by including a Base Attack Bonus AND a hit-table/matrix. And converting AC on the fly is simple, just subtract from 19. But, yeah. BAB is just THAC0 backwards, or something. The math would be the same if there weren't AC limits in AD&D.

  4. I dunno, I find that it works ok exactly the same. Either way, I need to determine the target number needed on the d20n BEFORE the d20 is rolled, to avoid painful post-roll calculation (worst with multiple attacks!)

    With descending AC I have to deduct THACO from AC to determine target number.
    With ascending AC I have to deduct to-hit bonus from AC to determine target number.

    Descending is a bit harder with high level PCs - negative ACs and often negative THAC0; I think it's slightly easier at low level.

  5. I've never tried adding AAC to my old school games. Neither have I ever understood the problem people have with descending AC. As a player I simply ask the DM "what's their armour class?" He tells me, my eyes momentarily flick down to the bottom of my character sheet to locate the number needed and I attempt to roll that number or higher. This doesn't even require any thought, let alone calculation. All I have to do is move my eyeballs slightly.

    As a DM I have an additional couple of flicks of my eyeballs, they flick down to the table to check attackers level...flick across, defender's AC....flick down, number needed. And then I roll the dice. This might take me a second or two longer than as a player, and while I've had to do a teeny bit more thinking, once again I haven't had to do any calculation because the table has done it for me - and the result is right in front of my eyes on the back of my DM screen.

    Why would I want to add a string of numbers in my head? I'm too lazy for that. I honestly don't understand the problem. :-)

  6. I think descending armour class was one of the main things that put me off D&D when I first started gaming. I couldn't get my head around it and moved on to other games.

  7. I like using the tables - it's the no math version.

    1. Thank goodness, I'm not the only one. :-)

  8. After playing Champions for four years straight, it is really hard to get why people get so excited about such a trivial difference.

  9. Here is an interesting experiment (to me).
    Say that you are using ascending AC and you want your players to write down on their character sheet a based chance to hit an unarmoured opponent. You want this so the players can internalize the numbers and know their basic chances.
    So an unarmored opponent is AC 10.
    The player would start adding up their bonuses (say +2 str, +1 for level, +1 for some magic item) and substract that from 10
    So they write down their THAC10 is 6
    And as a GM you convert monsters AC by taking off 10 and describing it as a difficulty modifier. So a kobolds AC of 15 becomes a +5 difficulty modifier.
    The player takes their THAC10 of 6, adds 5 to get 11 and that is their target number to role.
    This system is what I liked about the older THAC0. It really has nothing to do with ascending or descending. It is more about how you make notation of the system, and where you do the math.

  10. The descending armor class approach still makes no sense to me at all. It's totally counter-intuitive. It is one of the things which led me to drop the original D&D after just a couple sessions. In terms of game design I really prefer an approach where armor absorbs damage rather than being factored into To Hit.

    1. I am in favour of ascending AC myself. But I believe it really is more on how the two systems are presented. Really, they are the same thing it is just hard to visualize.
      What if the terminology was changed to
      Your armor penalty?
      Everyone is assumed to be wearing battle gear and be relatively quick in reflexes. So, the baseline AC penalty is 0.
      If you wear something less... say chain mail, then your AC penalty is 5.
      If you wear noting, then your AC penalty is 9
      It makes a bit more sense to me when it is stated this way. Now, I am not saying it is better, just that its a trick of the mind what is intuitive.

  11. I favor ascending armor class, but I'm not a raging partisan. The deal breaker for me is alignment and especially alignment languages (yuck!!). If old school means lawful good grammar, then I'm not old school.

  12. I use both, depending on whether I feel like looking for the chart or doing the math or what the player understands.

  13. Descending AC isn't a deal breaker for me.

  14. I elected to use Ascending AC in Basic Fantasy RPG, not because of any worries about WoTC, but because I prefer it.

    (Also, I omitted alignment because I got sick of arguing about it decades ago...)


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