Why Descending AC?

Descending Armor Class is a trope of BX, but as new retro clones appear, you also see THAC0 and Ascending Armor classes. Those are all choices, but which is best depends on who and when you are. And to be honest, which one you pick makes no difference. 

Way...way... way... back... to the DMG for AD&D, AC had a different mechanic than simply beating a number. There was a chart or series of charts that had endpoints. Characters reached a certain level where it was simply listed as "level n+". For Fighters, at the first level, you needed a 25 to hit AC -10 and an 11 to hit AC 10. Going to the other end, it didn't matter how high your level was; there was just one line labeled "This level or over". There were bounds to the charts. 

But if you ignore boundaries, all three attack systems are basically the same. 

For descending AC, you could fill out the Attack Value Matrix on your character sheet like so: 

Except this tool was in the hands of the DM! You would tell your DM what you rolled, and what your bonuses were. 

It would be up to the DM to consult the chart and tell you if you hit. What number you really need to succeed is obscured. This makes B/X and AD&D e1 especially deadly because you don't know what you don't know. Also, the tables had steps or jumps in probability not so much to keep one guessing, but due to the boundaries set by the charts and the progression of classes.   

For THAC0, instead of using the chart, you'd figure out what you need to hit AC 0, then calculate what you need to hit. In this case, roll a d20, subtract your opponent's AC, and see if it was better than what you needed. The two issues with this method are: first, the probabilities are different, and second, the monster's AC isn't obscured at all. 

You could either calculate on the fly all the time or fill out the Attack Value Matrix. It didn't matter, except as before, the tables were often not listed on your character sheet, and it still felt like the DM was slightly obscuring the needed info to calculate a hit. 

For Accending AC, you roll a d20, add your bonuses, and compare that number to your opponent's AC. This is different because this is all on the players, not the DM. A chart isn't necessary at all. 

So, why was Descending Armor Class ever a thing? 

A lot of people would answer: "Wargames have charts, and that is simply the way it was done". That's true, not the whole story. 

It comes down to how you were taught math and WHEN. For people coming of age in the 1960, you'd have a very different way of learning math. Check out this video. 

Believe it or not, the audio of this video is from 1965 as an objection to what was called "New Math". New math was what was taught from 1965 on. Math teaching changes. If you played D&D in the 1970s, you have experienced 4 changes in how math was taught. 

So, when Gary Gygax learned math, he didn't learn like the youngsters today. But he knew what he was talking about. 

Ask yourself, what is 3+4? Virtually every adult has this fact memorized, and no real math occurs. Even if you use your fingers. 

We'll call this the 7 configuration. 

Or does it? 

Ask a young child the same thing. 

Literally, 3 and 4. 

They will probably hold up 4 fingers on one hand and 3 on the other. There will be a pause while they put down one figure from the 3 hand and put up another finger on the group of 4 hand. 

And we are back to the 7 configuration.

Ok. They did some math right there, but what exactly did they do? Can you show your work, like the video jokes about? 

Yes, but you need to think in terms of spaces, not numbers or fingers. Theoretically, everyone has 10 fingers. 

 

Most of the time, I have 10 fingers.

OR we have 10 places to record things... numbers usually. But it could be pips, or apples, or oranges. 

Ok. So what is the point? 

We are back to the young child. The young child did some sleight of hand. First, he or she held up 4 fingers, then 3 fingers, then showed you all of them together. Next, he moved one figure from one hand to the other, to land in the seven configuration. If you live in a different country, which fingers you show would probably be culturally different, but still showing 7 fingers between two hands.

Now, let's show the work: 

10+4=14
10-3=7
14-7=7

Did I just do addition with subtraction?

Yup. 

That Trad Math, if you will. To add and subtract, you have a boundary - 10 fingers to hold information. If your range is between -10 to 10, you never need more than 10 fingers. 

Let's take slightly large numbers to prove it works, with more than 10 slots. Consider 47+38. 

100+47=147
100-38=62
147-62=85

Notice that for bigger numbers, I need the place above it. In this case, for numbers between 1-99, I need the 100's place. 

That is very different from putting 47 on top of 38 on the page, adding 8+7 for 15, adding 4+3 for seven, shifting the 7 to the left to represent the 10s place, and adding 70+15 to get 85. Watch that video again. Tom Lehrer found New Math totally perplexing. And it IS to some people. 

We are missing a step. In 1989, there were the NCTM Standards, which were different standards than New Math and also very different from the Common Core. The order is Traditional Math, New Math, NCTM Standards, and Common Core. All of which you would have lived with if you played D&D in the 1970s. 

This is why there was a progression from Descending Armor Class, to THAC0 and finally Ascending Armor Class. AD&D and BX are in the transition period between Traditional Math and New Math. 1989 marks the transition between New Math and the NCTM Standards. And Third Edition D&D and above marks the transition between the NCTM Standard and Common Core. 

Funny how that all works, with the dates lining up so neatly. 

So at my table, Traditional Math is king, with Descending AC. At your table, I bet it's something else, and you will have to thank your math teachers for making you just as right as me. 

The Keep on the Borderlands 2025 Sessions - The One About Mechanics

This post is about some of the mechanics I use in Keep on the Borderlands. This module was contemporaneous with AD&D and came out just a bit before the Expert Boxed Set. No one would have had those rules at the time of B2’s publication, which creates all sorts of oddities. I personally use Old School Essentials by Necrotic Gnome over the original Basic and Expert rules because I was able to obtain them in hard copy. As of right now, the B/X rules are available in POD, so I will probably order these for nostalgic reasons. 

All of the links above go to DriveThruRPG. I earn from qualifying purchases.

Looking at the module, the map scales are poor. The Caves of Chaos combine both interior and exterior maps, but the transition between them is awkward. The interior maps are fine, yet the valley floor is a ridiculously tight space. I’ve covered these complaints elsewhere, and none of them are deal-breakers. I simply ignore what I want or come up with reasonable rules of thumb. About 99% of these adjustments favor the players, so they don’t object either.

The second issue is the wandering monsters. Every area lists specific wandering monsters, then claims that no reinforcements are possible. Elsewhere, the text mentions that new monsters will move into cleared areas of the caves. Some versions of the module even include a wandering monster table completely different from the earlier lists. What a mess! All of these ideas contradict one another.

Here’s what I do with these conflicting rules: I condense all the wandering monster lists down to creatures that actually appear in the module. Four times a day, I roll for wandering monsters: Sunrise, noon, sundown, and midnight. If the result matches a group that has been depleted, I treat it as reinforcements for that group’s location. 

If I roll a monster type that hasn’t taken losses, I use the reaction table. If the result is neutral, the newcomers move on. If it’s positive, they join the home team. Even if there are no losses to replace. They are evenly divided among all relevant locations. If the result is hostile, a fight breaks out between the newcomers and the cave’s inhabitants. I don’t bother running the combat; I simply roll damage for both sides. Nine times out of ten, the newcomers are wiped out, leaving their gear and treasure behind for the victors. Oddly, if there is a net loss of monsters, the survivors come out on top because they have better gear and treasures. 

The fun part is that the players get unpredictable new encounters without knowing where these monsters came from. Just like you. I’ve been rolling for reinforcements through all nine sessions so far, though I hadn’t mentioned it in my posts until now. 

There’s one catch to all this: you only roll while the game is in session. If a session lasts a day, that’s four rolls. If a time break occurs, for example, if the party retreats to the Keep, you don’t roll for that downtime. Rolling for every day that passes, regardless of player activity, would flood the area with monsters. Wandering monsters should be a randomized response to player action; if the players are inactive, no roll should be made.

The party has been here for 5 days, for 20 wandering monster rolls. Monsters are rolling into the area due to all the strife. Here are the results, in order of appearance: 

Giant Rats (4), Owlbear (1), Kobolds (10), More Rats (5), Goblins (3), Goblins (6), and a group of traders. 

The rats and Owlbear all gravitated to Cave G, more than restoring that area. The party saw this happen, but missed the rats. The goblins and kobolds went to their known haunts and became reinforcements; the party probably saw this, but didn't understand these were new creatures and not the remaining survivors.  

I decided to give the trader a chance to live by generating a party traveling with a high-level magic user. You can use the same generator here. I then deleted every character over the second level, leaving 6 characters. 

For this run through the Caves of Chaos, the players did something unusual. They haven’t really fought the kobolds. Kobolds are generally weak and tend to attract player aggression. I’ve played them as opportunists, striking only when the players seem weak or distracted. Since I’ve run this module half a dozen times before, I wanted to avoid another head-on clash with the kobolds. I already know how that plays out.

The next session will start with the appearance of the wander party. 

If you like the goblin and kobold figures, you can find them in your local hobby shop or perhaps on Amazon, here and here. They even have an Owlbear. As an Amazon Associate, I earn from qualifying purchases. 

Game Scale - Down the Rabbit Hole - Part 1

As mentioned last time, I am prototyping a science fiction game. 

Before I get to the fun of developing characters and equipment, I like to think about scales. Usually, the first scale I like to work with is "How big is it?" I have always hated the D&D weight and encumbrance scale but in certain ways it makes sense. 

A gold coin is heavy, this is sort of appealing from a DM's point of view. "How big?" is connected to "How much money?". It's not perfect but it does make sense. 

Since I am doing Sci-Fi, I want to leverage SI units. So meters and kilograms are usually what the players encounter. I don't have to come up with my own units. Made-up units nearly always sound silly. How much damage can the words like "Parsec" or "Cubits" do?

Don't answer that.  

The rabbit is out of the
hole.

In thinking about this, I wanted to go down the economic rabbit hole first. It was surprisingly, easy but also comes with its own problems: 

1. Cost doesn't equate to size or weight. 
2. What do I call space money? 
3. Space money sucks as a name. 
4. Will I use creeping capitals: "Space Money" vs. "space money"? 
5. What color is it?  

I decided to name the unit of money "Credits". It is a classic and doesn't suck like "Space Money". Credits are used to buy average, daily stuff. A loaf of bread, a bullet, a comb are all right around one credit each. 

Players won't want any of that, they want lasers, robots, aircars, fighters, and spaceships. One of the wacky things with letting characters have all of these things is that the scale rapidly gets into the millions or even billions of Space mone... er, credits. I hate math that gets out of control.  

The first issue I need to address is that credits are "shiney". It's sort of a color. (There is a whole different rabbit hole about most cultures not wanting to call the sky "blue", but "bright" or "shiny", like bronze. Feel free to climb into that rabbit hole on your own time. Here is a link to get you started.) 

Next, we need a scale to prevent players from yanking their hair out jumping from "How do I buy lunch?" to "How do I buy a spaceship?". 

SI units to the rescue. Will just use credits, kilo credits, mega credits (starting to sound silly..._ giga credits (somehow less silly), and so on:

• Credits (Cr) = Base unit
• Kilo Credits (kCr) = 1,000 Cr
• Mega Credits (MCr) = 1,000,000 Cr (1 million)
• Giga Credits (GCr) = 1,000,000,000 Cr (1 billion)
• Tera Credits (TCr) = 1,000,000,000,000 Cr (1 trillion)
• Peta Credits (PCr) = 1,000,000,000,000,000 Cr (1 quadrillion)

I haven't used AI chats to create content, but I decided to be lazy today and leverage it. ChatGPT did the chart above so I didn't have to do math. Even better, I didn't even sanity-check it. I have no one to blame but my lazy ass self. 

Anyway, I asked GTP Chat to compare that scale to a couple of different real things. A 60,000,000 credit vehicle is best measured in mega credits: 60 mcr. A space shuttle is 1.7 gcr. A motorcycle is 12 kcr. 

This chart gives a base of credits and 5 different scaling factors. That isn't much more difficult than D&D's copper, electrum, silver, gold, and platinum conversions. That will allow me to use 6 different colored tokens to scale things. Yes, I am ignoring that I need 1000 of one colored token to get to the next step in the scale. 

The nice bit about this scale is it is based on reality. The GDP of planet Earth is around 0.1 pcr. We aren't at most science fiction levels of technology so we don't produce a whole peta credit worth of stuff in a year. 

There is a time component to asking how long it takes to build a spaceship without starving everyone on the planet. You can build the Deathstar, but it takes a couple of years or more. This is why they aren't left sitting on a used spaceship lot but the Serenity is available at your local used spaceship lot. 

This time component is nice and I want to reuse this concept in my next post about combat scale. This is another headache for sci-fi: "What happens when a spaceship snipes individuals on the ground?" This will be my next post. 

The bad part is I thought I would be talking "game scale" like distances and weights, and this doesn't do it. A million-dollar diamond ring and a million-dollar airplane are wildly different sizes. An acre of desert could be less than an acre of farmland. A bag of feathers and a bag of lead are wildly different to lift. Nothing matches or scales nicely. I'll have to work on that bit. 

Anyway, thank you for climbing into this rabbit hole with me. I plan on having a whole series of posts as I develop this game.