XP: The Big Switch, Pt. 3

One final observation on the difference between the monster XP award system between Original Vol-1 (linear in HD) and Revised Sup-I (parabolic in HD up to name level). Let's run our updated Arena simulator program under both these XP award systems. Parameters in use here are: 10,000 fighters, 200 cycles of one-on-one man-vs-monster combat, expected treasure awards being added, no special abilities simulated (so: somewhat safer for the men), -2 modifier given to the random monster level die.

Here's the resulting fighter population with the Revised (Sup-I) XP system:

And here's the population generated under the Original (Vol-1) system:

So this reiterates the expected finding that the Original (linear) XP system is much more generous to low-level characters (by a factor of fully ×10 XP value), and so we get somewhat more lower-level characters successfully leveling up, or in other words, the curve for advancing levels is noticeably more gentle.

Interpolating the curve at lower levels for the Revised system gives an advancement function of about y = k e^(-1.4x) (where x is the level, k the 0-level men-at-arms population, and y the population at any other level), or approximately dividing by 4 at each sequential level. In contrast, the Original system generates a simpler advancement function of close to y = k e^(-x), or approximately dividing by 3 at each sequential level.

Moreover, looking at the Original XP system, compare several possibilities for a modifier to the "Monster Determination and Level of Monster Matrix" (Vol-3, p. 10), versus the prescribed higher-level leader proportions from encounters with Men (Vol-2, p. 5):

We see that a modifier of -2 to the random-monster die roll in the Arena gives the best match (least sum-squared difference) to the leadership proportions given in Vol-2 (whereas previously under the Revised XP system we saw that a modifiers of -3 or even -4 from book was necessary). So in other words: Taken as a whole, the Original XP awards are closer to presenting an overall rational system of demographics in D&D.

I suppose the most important consideration is: How fast do you want your PCs leveling up, in terms of number of encounters faced? (And this was in fact used as the starting axiom for the 3E XP system, for example.) If you use the Original linear system, you will have PCs advancing through the lower levels somewhat more rapidly than many of us are accustomed to in D&D. In the period when Gygax was running pickup games in his basement every night of the week, perhaps he legitimately felt the need to slow down advancement, so that people weren't gaining multiple levels within a week of play. But for those of us who now play somewhat less frequently, perhaps the original system from Vol-1 -- which is actually a better representation of the real "value" of a monster, and also a more generally coherent demographic system, and also a lot simpler -- is still the more encouraging one.

Get the updated Java source code to the Arena program (v. 106) here.


  1. So I downloaded the Arena simulator and extracted it... which file do I open? The .gpj file? What the heck is that? I've never seen that file extension before.

  2. Well, this sort of assumes that someone is set up to compile and run Java source code on a regular basis. The .gpj is a project file for the jGRASP development environment (which I think most people would just ignore). If you want to set yourself up for that you could download and install Java, the Java Development Kit, and possibly jGRASP (all free), and then start running and modifying that code. If you want more info, I can provide specific links.

  3. Thanks! I have JRE, but I can get the JDK easily enough. Appreciate it!

  4. Okay, I'm dumb. I downloaded JDK, but the most I can manage is to get little console windows to open - stuff happens very fast in them and then they close. I've clicked on all the .java files, but none of them seem to do anything different for me.

    I clearly have no idea what I am doing.

    1. Well, you're most of the way there already. Try installing jGRASP; I do think that environment is much easier to use. It's designed as an educational tool from Auburn University -- probably some other folks would laugh at me using it, but it makes stuff pretty easy to get at.

      Once you have jGRASP installed, open the project file (GPJ), then the green "+" icon to compile everything, then the red "running man" icon to run everything. At that point you can look at the fields at the top of the Arena.java code file and adjust those to run your own experiments. :-)

      See bottom of the page here (survey is optional, feel free to skip it):

      jGRASP Downloads

  5. @ Delta:

    This is pretty good stuff. When I wrote Five Ancient Kingdoms, I went back to OE (linear) calculations for determination of monster XP, and after reading these posts I'm glad I did (seeing some retroactive justifications here).

    'Course I was just going for simplicity.
    ; )

  6. I think you hit it on the head.
    "How fast do you want your PCs leveling up, in terms of number of encounters faced?"
    For experienced players getting through those lower levels quickly is probably a good thing. For newer players I generally like to give them some extra time to get the hang of things before leveling up.
    But maybe that's why 1st to 2nd level is 2000 XP?

    1. I can definitely see an argument for that. The other thing is most folks I know these days can't game every week, so I wouldn't be offended at new players gaining a level every session or two to get a taste for that reward (before it slows down at the mid-levels).

      I noticed in the Holmes book last night the assumption that PCs would level up every 6-12 adventures (assuming ones where significant treasure was returned), which mentally I converted to once every 6 months with the group that I currently play with (as a PC) biweekly.

  7. Another thing I don't mind with the more generous leveling: If a high-level character is energy-drained by undead down to low levels, it's a bit more convenient to gain those levels back rapidly.