Quote from: Shasarak on March 02, 2021, 12:19:53 AM
If you have a Bab of +3 and are attacking someone with an AC of 15 then you need to roll (15-3) a 12 to hit.

Yeah I always do that calculation when running tabletop. So in effect BAB & THAC0 work out exactly the same in complexity for me.

I prefer d20 + mod vs TN as the base mechanic because it is easier to explain.  I run into a lot of players that want to understand how it is supposed to work.  This is in contrast to my high school days using Basic/Expert and AD&D where I had two kinds of players:

- Those good at math and systems, such that it didn't matter what system we used.
- Those that freaked out about "Math!" in a game if it used any calculations at all.

The chart written on your own (homemade) character sheet worked very well for those players.  The first group internalized the math almost immediately.  The chart worked as well as anything else, as they quickly memorized it.  For the second group, it was the difference in playing and not playing.  Moreover, we had a few that stuck with it long enough that they also internalized the math of the chart, which made "Math!" less threatening to them.  In once case, a math teacher shared with me that they had noticed an improvement in the classroom in that regard.  No, AD&D didn't help the kid do better Algebra.  It helped him quit wasting a lot of energy worrying about it so that he could get  on with the job of learning it.

Since, I've run into three players with this "Math!" fear.  Two dropped out fairly quickly, as the game just wasn't for them for many reasons.  For the other, I wrote out a little chart of the d20 + Mod vs TN numbers they were likely to encounter ...

I also think that d20+mod vs. TN can get within 2.5% of the probability of any other single die check and any multiple die check with a fixed target number and no margin of success element is another part of why it was able to so easily replace a lot the earlier D&D mechanics.

It's not identical to those other polyhedrals, but within 2% on a flat distribution is close enough for all but the most math focused.

Offhand, the only mechanic I can even think of in TSR-era D&D that a d20+mod check couldn't emulate well is the Reaction Roll (which probably explains all the issues with the Diplomacy skill which was the analogue in all the WotC editions).

5e also seems to have finally figured out to that by keeping the target numbers low enough, you can also keep the modifiers mostly in the single digits for easy math.

This was a lesson my own group learned midway through 4E when we implemented a house rule to remove the per level scaling to attack bonuses and defenses because, regardless of the current modifier/DC, the actual result needed on the die didn't really change (and deviations from the die result needed was entirely the result of relative level).

This worked its way into my own system where attack bonuses and defenses stayed virtually fixed (about +2 over the course of 15 levels), but damage/hit points scaled linearly.

You get the same probabilities with +27 vs. AC 36 and +7 vs. AC 16, but with the latter the math is, at worst, single digits and sometimes doesn't even require addition at all (i.e. you roll a 16 or better on the die you don't even bother adding the bonus because the die is already beating the AC). Monsters also stay threats just by adding more of them to scale up the group's damage and hit points.

The point though is that, with a softcap of 21 on defenses (hardcap is 24 with min-maxing that will gimp you in other ways) and a softcap of +9 to attack rolls (hardcap is +13 if you're willing to be gimped elsewhere) and most things being more like 15-18 and +5-8... the d20+mods vs. TN provides good results without any complex math.

So much so that I think it is possible to argue that it is objectively superior as a mechanic to both the simultaneous use of multiple unconnected d20-based resolution systems found in TSR-era D&D (i.e. use THAC0/tables for attacks + roll vs. TN for saves + roll as close to attribute without going over for skills) and to 3e/4E's high double digit modifiers and DCs math.

This isn't to say that one can't appreciate the craftsmanship that went into a Model-A pickup truck; but to argue that the Model-A is mechanically superior to say, a 2003 Ford F-150 pickup, would be ludicrous (even the "easier to repair" argument fails as almost any part you need for a Model-A has to be custom fabricated by a small number of specialty manufacturers... as I've learned trying to source parts for my Dad's Model-A).

My Dad loves taking country drives (or appearing in local parades) with his Model-A, but he doesn't even think about trying to do any serious work with it; that's what the F-150 is for.

I feel the same about game mechanics. Using the old charts and clunky mechanics are great for a trip down memory lane, but they're not remotely what I'd choose for a regular campaign when there are other mechanics that do the job in ways that are much easier for players like my niece and godkods to grok.

Quote from: Chris24601 on March 02, 2021, 12:33:46 PM
I also think that d20+mod vs. TN can get within 2.5% of the probability of any other single die check and any multiple die check with a fixed target number and no margin of success element is another part of why it was able to so easily replace a lot the earlier D&D mechanics.

In the various classic edit the vast majority of other checks are percentile and the modifiers are in +5% increments.

So in  my Majestic Fantasy rules I converted them all to various flavors of 1d20 roll high. A 70% magic resistance became a 1d20 roll + 14. If the roll was 21 or higher the spell was resisted.

If anybody interested in the interplay of AC, Hit points, damages, and bonus to hit. I created a D&D combat simulator along with instruction on how to use it with any edition.

https://www.batintheattic.com/dnd_combat/

For example +1 to hit difference between to fighters with the same AC and same HP and the same damage will transform a 50%-50% fight to a 60%-40%. The same for +1 AC

However +1 damage takes the odds to 71% to 29% in favor of the fighter with the +1 damage bonus. If you just increase # of attacks to 2 from 3/2 then the odds shift to 81% to 19%.

For managing a campaign this simulator is worse than useless it is deceptive as it doesn't account for circumstances. Combat is not just two opponents whacking away at each other.

It is useful if you into trying to muck around the system and want to get a sense of scale and the relative impact of doing X over Y in the mechanics.

One thing this convinced me to do is follow 5e's lead in capping magic item bonus at +3 instead of the traditional +5.

Quote from: Chris24601 on March 01, 2021, 07:50:51 PM
My experience with THAC0 was not THACO - AC = TN; because that would require you to KNOW the AC ahead of time.

It's interesting to me that this little quirk in how we played makes such a large impact on the amount of math employed during the game.

Seems to me a good reason in itself to reveal the target AC to players; for me I guess it outweighs the ... increased suspense I guess? I never really got the benefit of hiding the AC, just the discomfort. It never felt particularly realistic that a trained warrior couldn't estimate the target's AC beforehand -- they can see where they need to put the blade and how difficult it will be. And I would think that same fighter could pinpoint the AC, including magical bonuses, after the first attack (when their blow unexpectedly deflects off the soft-looking flesh, etc.)

Quote from: Zalman on March 02, 2021, 01:36:46 PM

Quote from: Chris24601 on March 01, 2021, 07:50:51 PM
My experience with THAC0 was not THACO - AC = TN; because that would require you to KNOW the AC ahead of time.

It's interesting to me that this little quirk in how we played makes such a large impact on the amount of math employed during the game.

Seems to me a good reason in itself to reveal the target AC to players; for me I guess it outweighs the ... increased suspense I guess? I never really got the benefit of hiding the AC, just the discomfort. It never felt particularly realistic that a trained warrior couldn't estimate the target's AC beforehand -- they can see where they need to put the blade and how difficult it will be. And I would think that same fighter could pinpoint the AC, including magical bonuses, after the first attack (when their blow unexpectedly deflects off the soft-looking flesh, etc.)

I think in most fights, 80% of the utility of the players not knowing the exact AC all happens in the first round. 

Players collectively:  We got an 8, 11, 15, 17, 19,  and 22 on our hits. 

GM:  The last one hit.
Players:  Yikes!

or GM: All but the first hit.
Players:  Piece of cake!

or GM:  Three hits.
Players:  About what we expected, maybe a little tougher.

There's a little remaining marginal utility in the exact number being hidden in those scenarios and a few others, but it really is quite marginal. I guess if none of the hits connect, the players knowing that it is higher than 22 but not how much higher could affect their immediate plans.  But it is already clear that "Yikes" is the operative expression.

Quote from: S'mon on March 02, 2021, 05:21:27 AM

Quote from: Shasarak on March 02, 2021, 12:19:53 AM
If you have a Bab of +3 and are attacking someone with an AC of 15 then you need to roll (15-3) a 12 to hit.

Yeah I always do that calculation when running tabletop. So in effect BAB & THAC0 work out exactly the same in complexity for me.

Thats maths for you.  Always calculating to the same value.

Quote from: estar on March 02, 2021, 01:07:37 AM
I also wrote about how I handled campaign. While I may have changed system I evolved how I ran things. The heart of what I do today can found in the campaigns I ran in 1980.

What is that? You can find the short version in my Blackmarsh setting.
https://www.batintheattic.com/downloads/blackmarsh_srd.zip

Great post, and I had to say . . . thanks for Blackmarsh! I haven't actually used it at the table, but it's an inspiring document and led me to do more hexmapping of my own campaign worlds. It's a great example of how I think a campaign setting should be.

Quote from: Steven Mitchell on March 02, 2021, 01:58:49 PM

Quote from: Zalman on March 02, 2021, 01:36:46 PM

Quote from: Chris24601 on March 01, 2021, 07:50:51 PM
My experience with THAC0 was not THACO - AC = TN; because that would require you to KNOW the AC ahead of time.

It's interesting to me that this little quirk in how we played makes such a large impact on the amount of math employed during the game.

Seems to me a good reason in itself to reveal the target AC to players; for me I guess it outweighs the ... increased suspense I guess? I never really got the benefit of hiding the AC, just the discomfort. It never felt particularly realistic that a trained warrior couldn't estimate the target's AC beforehand -- they can see where they need to put the blade and how difficult it will be. And I would think that same fighter could pinpoint the AC, including magical bonuses, after the first attack (when their blow unexpectedly deflects off the soft-looking flesh, etc.)

I think in most fights, 80% of the utility of the players not knowing the exact AC all happens in the first round. 

Players collectively:  We got an 8, 11, 15, 17, 19,  and 22 on our hits. 

GM:  The last one hit.
Players:  Yikes!

or GM: All but the first hit.
Players:  Piece of cake!

or GM:  Three hits.
Players:  About what we expected, maybe a little tougher.

There's a little remaining marginal utility in the exact number being hidden in those scenarios and a few others, but it really is quite marginal. I guess if none of the hits connect, the players knowing that it is higher than 22 but not how much higher could affect their immediate plans.  But it is already clear that "Yikes" is the operative expression.

Hm, I get that most of the time players figure out the AC after the first round, but I'm missing the "utility" part. What benefit is gained by hiding it for the first round? I haven't noticed it particularly increases the excitement or engagement in my games, maybe you've seen differently.

Quote from: Zalman on March 03, 2021, 12:23:34 PM

Hm, I get that most of the time players figure out the AC after the first round, but I'm missing the "utility" part. What benefit is gained by hiding it for the first round? I haven't noticed it particularly increases the excitement or engagement in my games, maybe you've seen differently.

I do see a bit of nervousness on the first round due to not knowing the AC.  This gets magnified if there are a lot of misses or hits in that first round.  Plus, with uncertainty comes some decisions.  I've seen players decide to retreat based on the outcome of that first round (when maybe the didn't need to) and the opposite as well. 

My main point though, using "80% utility," is that whatever utility any group gets from the players not knowing the AC (whether a little or a lot), you get most of it that first round. 

I didn't mention that I also have a strong bias towards mechanics speeding up a combat progresses, because I think this naturally leads to more enjoyable fights.  I don't mind some "freeze frame" type descriptions at the climatic moment, but I want that coming from the GM, not the mechanics.  So I've not only got a reason to not particularly value the hidden AC the longer the fight goes, I've got a positive reason for speeding up mechanical resolution as the fight goes.  Thus, I often just tell the players the AC they need after the 1st round, 2nd or 3rd at most.

Quote from: Steven Mitchell on March 03, 2021, 01:30:17 PM

Quote from: Zalman on March 03, 2021, 12:23:34 PM

Hm, I get that most of the time players figure out the AC after the first round, but I'm missing the "utility" part. What benefit is gained by hiding it for the first round? I haven't noticed it particularly increases the excitement or engagement in my games, maybe you've seen differently.

I do see a bit of nervousness on the first round due to not knowing the AC.  This gets magnified if there are a lot of misses or hits in that first round.  Plus, with uncertainty comes some decisions.  I've seen players decide to retreat based on the outcome of that first round (when maybe the didn't need to) and the opposite as well. 

Another point: The nervousness will still occur, even if the DM calls out the monster's AC before the players roll. That's because the DM isn't going to call out the number until the players have already made the commitment to attack, so they have to make the most important decision without knowing the monster's AC. I've played with hidden ACs, and think the value is basically negligible.

It is much better to create nervousness from uncertainty regarding what a known monster may or may not do, than it is to rely on math uncertainty which only goes so far

Down the latter road lies the lazy DMing of reskinning monsters in the vain hope to recreate ignorance on an encounter-by-encounter basis.  While the former approach allows the monster itself to be known, as that is the least important bit of information

You are not scared of bears in the woods, crocodiles in certain rivers, or big cats where they are found, because you're an ignorant rube who's been kept from the collective memory of humanity

Semi-related to the point about uncertainty above is another advantage of "d20+mods vs. TN" over THAC0 that I first encountered when driven out AD&D and into Palladium; the ease of resolving opposed actions by making the TN another d20+mods roll.

The feeling of depth that getting to roll your defense (and opponent's defense likewise being variable) added to combat had just the right feel for me at that time. It also "hides" the monsters defenses by not having it be a fixed value and, if the GM isn't rolling in the open the players have to guess whether an announced total is due to skill or luck.

This isn't to say you can't do opposed attack or skill checks in AD&D; just that there's more math involved... typically rolling then determining a margin from the result and comparing it to the margin of the other roll. But that's nowhere near the efficiency of just "roll total vs. roll total; high result wins" (ties breaking results specific to each system).

So add that as yet another benefit to the "d20+mods" talent stack. It makes checks like hide and move silently vs. creatures with superior senses as simple as comparing two rolls and I've often found increased buy-ins during combat in systems where players get to do something in response to an attack even if, mechanically, its really just 1d20+mods-1d20 vs. target's defense mod and could be handled in a single roll.

It pretty much falls into that "advantage/disadvantage" mechanic category of its feel (giving a sense of having some control over your defense) being more important than the efficiency of the mechanic. +/-5 would have just about the same or better effect on most checks as roll twice and use better/worse, but the FEEL of a successful "save vs. failure" trumps the logic in play. In the same way, no one remembers the times you rolled a 9-12 on the die defense for a defense... the remember the time they rolled a natural 20 and avoided a deadly blow (and also the amusing times when they rolled horribly, but the attacker rolled even worse).