Thoughts on Measuring Peril

Benjamin Gauronskas was kind enough to give me a shout-out on his blog Let’s GURPS, saying that he likes the ridiculously large array of adventure-creation tables I posted yesterday.  Thanks, Ben!

(Warning: the rest of this post gets pretty technical – fellow GURPSheads only!)

He also makes an interesting point about my choice to use “N” as a measure – he says he would have used CER, instead.  This is an intriguing idea.  Let’s explore it a little.

First, what are these terms?

“N” is simply a GURPS shorthand for “The number of PCs in the group” (pretty much).  It first appeared in Matt Rigsby’s Dungeon Fantasy Adventures 1: Mirror of the Fire Demon. It’s a handy way to make the size of encounters dependent on the size of the PC group.  You can say “this encounter will be with N Ogres,  or 2N Orcs,  or N/2 Giants” – and then the encounter is automatically going to scale up or down in size, depending on the number of PCs.  From the perspective of someone writing a procedural system (like I am), that’s really handy!

“CER”, or “Challenge Effectiveness Rating,” was invented by Christopher Rice of Ravens n’ Pennies fame. It first appeared in his article “It’s a Threat!”, in Pyramid #3/77: Combat.  It’s a more sophisticated measure than “N,”  since it gives you a way to eyeball the overall combat effectiveness of any group of combatants, taking into account their actual capabilities as well as their numbers.  I like Christopher Rice’s work a lot, and CER is no exception – it’s a good idea, extremely well executed. Where N measures quantity only, CER manages to measure quality and quantity.  This means that CER is a much more precise way to calibrate encounters than N is – though it’s also more complex, and obviously requires more calculation.

So why did I use N rather than CER?  Well, there’s the fact that N is really easy to use – by comparison, CER takes a lot of calculation.  But that’s not really the main reason.  The main reason is that I already had a way to rate encounters by “quality”, as it were: my new system of Peril ratings .   (Peril is a bit like B.A.D. from the GURPS Action line, for those who are familiar with it)

In my system, Peril measures quality, and N measures quantity.  Splitting them up might seem to make things more complicated (wouldn’t it be simpler to roll them all into one calculation, as in CER?), but it actually makes thing easier for me, since treating them separately means that no complex calculations are necessary: each measure is very simple to use.

Treating Peril as its own thing also makes for some fun, hard choices between risk and reward during the game.  Adventures, wilderness journeys, dungeons, monsters etc are rated by Peril – and so are rewards and treasures.  The PCs can choose to head into whatever Peril they feel like  – they can play it safe, for less chance of decent treasure, or they can head into more dangerous areas in search of greater rewards.

There are also a whole bunch of moments in the system when the Peril gets adjusted whether the players like it or not.  For instance, you might arrive at the Forgotten Temple of the Tiger Princess, thinking it’s going to be a cakewalk, only to discover that it’s much more dangerous than you’ve been led to believe.  Or you might find that The Crypt of the Deathlord is a lot less dangerous than its name suggests – and if your employer thinks the dangers are greater than they are, and he/she might end up overpaying you.  And so on.  All of that can be lots of fun!

And that’s why I chose to use N and Peril together, rather than CER.




4 thoughts on “Thoughts on Measuring Peril

  1. Interesting thought. I might need to look at it again a bit closer; I was thinking of the peril as something that could be used as a modifier to the N value so that with a low peril, you might multiply the n value by a number less than 1, and with a high peril you might multiply it by a number greater than 1.

    I enjoy playing with procedural tables though, and I like the look of yours, but haven’t had a practical need to use it yet… I have an adventure all prepped up already for my group, but somehow game night has been pushed back two weeks now.

    On a similar note, I’ve enjoyed this system too:
    It’s a neat idea that helps design a map for a dungeon by throwing polyhedral dice *on top* of a piece of paper, and looking up what the dice roll means is at that location, while also organically having teams of delvers, miners, and bad things building a structure. The free version of the PDF on that site has almost all the information you need to use it as well.


    1. Ah, I love How To Host a Dungeon! The dice-dropping method is heaps of fun.

      My condolences on game night being pushed back for two weeks – that’s always a bummer.

      Regarding how N and Peril interact: the system has them interact in different ways at different points. Here, in the adventure creation part of the system, they basically just govern Rewards – how much money your employer is offering you. Then they do multiply. But they work differently elsewhere. Monsters, for example, are rated by Peril: that governs how tough they are individually. But they also appear in multiples of N – so you can have your newbie solo hero heading into a fight with a Peril 1 Orc, or your big party of 8 very experienced PCs heading into a fight with 8 Peril 6 Orc warlords, depending – and both of those derive from precisely the same roll on one of the tables.

      Good luck with the next session!


  2. I’d suggest a somewhat different way of looking a this. “N” is a user-end tool and a relative measure of threat. The GM is presented with various options for opposition and is assured by the designer that some N-based number of opponents is suitable opposition for the adventurers who will encounter them. There are a lot of assumptions hidden behind N, and it has to be retooled for every batch of characters and monsters who might face them by means which are not inherent in or derivable from the measurement.

    CER is a designer-end tool and a (one would like to think) objective measure of threat. The designer can derive a measurement of the threat posed not just by monsters but by characters as well. CER ratings can then be compared to one another to produce match-ups.

    A designer might even use CER as a tool to arrive at N. For example, seeing that CER for a given monster is 33 and average CER for a batch of sample characters is 100, a designer may write that the adventurers encounter 3N of that monster with some hope that it’s an even fight.

    So, then, whether one uses N or CER depends on the audience. N, which uses small numbers, is a little easier to use. CER exposes a bit more of the thought process which goes into everything.


    1. But then, what would you know? 🙂 I’d much prefer to hear from someone who has given the matter some thought.

      More seriously, that’s a very clear (and, for me, clarifying) way of making the distinction. In a way, what I take you to be saying is that the designer *always* needs to do the calculations implicit in CER – whether by using the actual CER calculations, or (more often) just by eyeballing it – whereas N is a simplification that makes things easier for the end user by leaving those calculations “under the hood”, so to speak.

      That seems quite right. The designer can only write “Roll 1d6. This encounter is either (1-2) N Ogres, or (3-4) 2N Orcs, or (5-6) N/2 giants” if s/he’s already determined that the PCs are at a power level such that an appropriate challenge for a single PC is 1 ogre, or 2 orcs – or only 1/2 a giant.

      For what it’s worth, I guess the problem I’ve been trying to solve is kind of an odd one, since when you collapse the distinction between the GM and the Players, the distinction between “designer” and “end user” actually starts to seem a bit hazier sometimes too. It’s still a valid distinction- someone designs the system of tables, and other people play with them – but the players necessarily need to have more access to what’s under the hood than they did before. In a way, that’s why I liked the simplicity of N, but then had to supplement it with this new thing, Peril, that gives the system (and the players themselves) a slightly finer way to calibrate things to the desired power level.

      Thanks for your comment! The blog being in its first few days of existence, it’s great to have such fine comments (and commenters!) already.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s