The Alexandrian

Eclipse Phase - Posthuman StudiosA quick review for those unfamiliar with the Eclipse Phase system: It’s a percentile system where you need to roll equal to or under your skill level in order to succeed. If your roll a success, your margin of success is equal to the number you rolled on the dice. If you roll a failure, your margin of failure is equal to the number you rolled minus your skill level.

(So if your Fray skill is 45 and you roll 27, your margin of success is 27. If you roll 89, your margin of failure is 89 – 45 = 44.)

Playing Eclipse Phase at Gencon this year, I noticed once again the difficulty some people have grokking this method of “calculating” margin of success. Part of the problem is that it’s discordant with how venerable percentile systems like Call of Cthulhu calculate margin of success (by subtracting the number you rolled from your skill rating). And part of the problem is that Eclipse Phase actually swapped methods between subtracting numbers and reading the die roll between printings. (The post-Catalyst Labs versions of the game should really have been clearly labeled a Revised Edition, frankly.)

But laying all of that aside, the huge advantage of the “read the die” method of calculating margin of success is that it completely eliminates calculation at the table when calculating margin of success: All you have to do is look at the dice. When you can get everyone to grok that (and to report their rolls as “XX out of YY” instead of just “succcess”) it makes the game run with incredible smoothness. (Margins of failure still require calculation, but the system doesn’t use them nearly as often.)

Having concluded that there’s a huge upside to calculating margin of success like this, without further ado I present several different conceptual frameworks that can help you (or someone else) grok the concept:

  • Success starts at 00 and grows from there, so the higher you roll the better your success (assuming that you succeed).
  • It’s like blackjack: You want to get as close to your target number as possible without going over.
  • It’s like The Price is Right: The dice are naming a price and you want that price to be as close to the actual price (i.e., your skill rating) as possible.
  • Your skill rating is like a gravity well: Successes start far away at 00, but the closer they get to your gravity well the faster they go and the bigger the explosion when you punch that guy in the face.

(For some reason face punching always features heavily whenever I’m teaching a new system to people.)


Okay, now that you’ve grokked how Eclipse Phase does margins of succcess, let me strain your credibility by proposing a similar method for handling margin of failure in the system. (This is really just a random thought that occurred to me as I was writing out the above.)

The key point here is that the system (a) rarely cares about margin of failure and (b) when it does, it only cares if you missed by either 30 points or 60 points. (The former are referred to as “severe failures” and in my system cheat sheet I refer to the latter as “horrific failures”, although I don’t believe the rulebook ever gives a formal term for them.)

So the method here is really simple:

  • A roll of 70 or less is a severe failure
  • A roll of 40 or less is a horrific failure.

The system also has a handful of effects which are determined “per 10 margin of failure”. (For example, shock damage can knock you unconscious for 1 round per 10 MoF.) To calculate that, simply subtract the tens digit of your result from 9. (So if you roll 77, you would be shocked for 9 – 7 = 2 rounds.)

If you’re looking for a conceptual framework, think of failure as emanating from 99 and growing in magnitude. Note, too, that higher is always better with this system: A higher success is a better success; a higher failure is a better failure. What my mind initially tries to interpret as a discontinuity actually makes sense if you just imagine success and failure emanating from opposite ends of the spectrum while the outcome is a linear comparison to your skill rating.

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7 Responses to “Thought of the Day – Margin of Success in Eclipse Phase”

  1. John says:

    Sorry for the off-topic, but I wanted to comment that it’s been nice to have some more frequent updates to this site. I hope life circumstances remain such that you can keep it up 😉 Also, my group is about to crack open the 5e starter set to give the new system a test, and I’m eagerly awaiting your thoughts on 5e at some point.

    On topic, the Price is Right analogy finally made what you were explaining click for me. I know you’ve been singing the systems praises, so I’ll definitely have to give it a try eventually.

  2. Auroch says:

    Another way of thinking about this mechanic, which I think works better with high numbers being bigger failures: The higher the number, the more extreme things get. The higher your skill, the more of that you can handle. So an unskilled character can only handle things if they stay very simple, but a skilled character can live dangerously and get more bang for their buck while staying on top of the situation.

  3. Justin Alexander says:

    @John: I’m also hoping to crack 5E soon, but it may be awhile. I’ve got ongoing Numenera, D&D 3.5, and Trail of Cthulhu campaigns running at the moment. That plus getting up to speed on The Strange for the con and demo scenarios I’m running has been chewing up most of my gaming head space.

  4. Will says:

    MoS was actually changed a while back in Core Rulebook errata(the phrase used is “to be more like Blackjack”). Now, your MoS/MoF is just the number you roll.

  5. Will says:

    …disregard previous comment. I sort of…read the opening paragraph of this post(incorrectly) and jumped right down to the comment section.

    I am everything that is wrong with the internet.

  6. Jeff Heikkinen says:

    I greatly prefer the “just read the number on the $*&^ing dice” method, but they shouldn’t call it “margin of success” since it’s not actually the amount you succeed by. That’s probably most of the confusion you mention early on right there.

  7. Leland J. Tankersley says:

    I haven’t played Eclipse Phase, but I did download and read it based on Justin’s recommendation a while back. They do a lot of stuff I like with the basic d% skill mechanic. My favorite little detail is that when you roll doubles it denotes a special success or failure — it nicely captures the greater likelihood of a special success with higher skill level (and of special failure with lower skill level) without requiring any math.

    @Jeff – I agree that margin of success is kind of a weird name. I’d suggest “degree of success [failure]” might be better. But really, you don’t want to be spouting “what’s your degree of success?” at the table anyway — “what’d you roll?” is more my speed.

    Thinking about it now, I think I’d want to say that high rolls are always better than low rolls, within a given result domain. That is, when you succeed you want the dice to be the highest possible value and still be a success (that shows off how good you are, to be able to succeed with a roll like that). And when you fail, you don’t want the dice to be a low number (only a clod would fail with a roll of 22, whereas there’s no shame in failing with a 97).

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