[Peter Knutsen]

I have a model for Night Vision and Colour Vision, in Sagatafl. It's better than nothing, but not by much. And that bothers me.

So I'm wondering if a few of you want to read my description of how Sense rolls work, and see if you can think of a different implementation from the one I use for regular Senses (including Vision), where everything works fine.



Sense rolls use the normal Sagatafl roll mechanic, with the added tweak that all Sense rolls use the Safe Roll rule, meaning that they can't Fumble. No matter how badly you roll, you can't do worse than failure, the absence of detection-of-stimuli. (Some other rolls can also be Safe Rolls, usually at the GM's call, as per his sense of realism, or sometimes the rules will probably say outright that certain rolls should be Safe.)

You roll a number of twelve-siders equal to the stat rolled for, the attribute or skill or sub-attribute or "derived", or in this case the Sense.

Each one that equals or exceeds the Roll Difficulty (RD) is a Success. More Successes are usually better, and of course they are more desirable in an Opposed Roll (e.g. Hearing vs Stealth Skill). If you get no Successes then you have a failure, or possibly a Fumble, except Sense rolls are Safe Roll so it's always just a failure (no "Ow! I sprained my nostrils!").

An average Human has a Perception of 3, with about 16% of the population being Perception 4, and much fewer being better than that, and the maximum being Perception 9, making you one-in-a-billion in world demographic terms, and of course exemplified by Sherlock Holmes. Below-average Perception can also occur in Human biological variety, about 7% are Perception 2, and about 0.15% are Perception 1, with lower values being rare.

Characters can have different Perception values for different Senses; this fuctioning as a sort of sub-Attribute, for instance one character can be very inclined to vision, so he's Perception 4 but Vision 5. I'm either slightly inclined to Hearing or slightly disinclined to Vision, so either Perception 4 and Vision 3, or more likely Perception 3 and Hearing 4.

It'd be quite reasonable to say that Leonardo da Vinci, in addition to being Intelligence 9, also was Vision 8 or even 9, in spite of not having quite such an extreme overall Perception value (maybe only 6 or perhaps 7). He really, really cared about that Sense.

Different Sense values represent fixed permanent inclinations, possible due to neuro-structure, or formative experiences in early childhood. You can't train Attributes or sub-Attributes, or Senses.

Sensory acuity is handled via a different mechanic:
permanent modifiers to the Roll Difficulty of the roll.

Normal Humans have an RD modifier of +0 for each Sense (this means the baseline is Humans - it's not like Humans have a poor Sense of smell and dogs have a decent Sense of smell, but rather Humans as the norm have a decent Sense of smell and dogs then have a fantastically amazing Sense of smell), but individual Human specimens may have an RD bonus of -1, or in extreme cases even -2. It's quite common for some people to have one Sense that's more acute than average, and I've read once that the test pilot Chuck Yeager had really sharp vision, so that could be an example of -2.

Impaired Senses are of course also possible, a penalty of +1 or higher, potentially much higher. Another possibility again is that a Sense is completely absent, as in Blind, Deaf or Anosmic. In this way there's a distiction between actually Blind and Legally Blind: The former sucks more.

The standard "adventuring" RD is 8, the equivalent of an unmodified roll in most roll-under systems (such as GURPS or Hero System). For everyday routine things you use a lower - easier - RD, even very low for the really easy. It's hard not to notice it if there's an elephant in the room. Everybody has in fact noticed it. They just pretend they haven't.

Rolling twelve-siders, you can't beat an RD of 13 or higher, meaning that for normal Humans, RD 13 is not perceivable ever, no matter how hard they try, how much they focus, how many time they roll. None of the twelve-siders you're rolling are ever going to come up 13.

(For Skills, you can Take Extra Time to lower the RD, and maybe with some other stat rolls too, but that doesn't work with Sense rolls.)

But of course individual Humans may have a -1 RD bonus to the relevant Sense, or in rarer cases a -2 RD bonus. Anything beyond that is superHuman, although Charles Darwin doesn't care about that. Lots of animals have superHuman Senses, with bonuses as high as -5 or -6, maybe even -7 or -8. A normal dog might be Smell -5 RD and a blood hound Smell -6 RD (most animals species also have an average Perception of 4, slightly higher than the 3 of Humans), while a cat would be Smell -4 RD I think. Dogs being a very scent-based species, they also probably have a raised average Perception (Smell) value of 5 (and possibly 6 for blood hounds, although that sounds a bit extreme to me), whereas cats are only Perception 4.

This means that Sherlock Holmes with his Perception 9 cannot notice an RD 13 scent, or an RD 13 sound, or an RD 13 visual stimuli, ever, whereas if he had a dog companion, a Familiar or something, it would have a fairly high probability of noticing even an RD 14 or 15 scent or sound, even if it has a Perception as low as 5 (or more appropriately for a pet of Holmes, 6).

Another Human with a keen Sense of smell (-1 RD bonus) might notice the RD 13 scent, but it's not likely, and he'd never notice the RD 14 scent.

Strength of stimuli also raises RD, of course, e.g. distiance for most Senses.

One further rule is that all characers have a Casual Perception modifier, which is applied to all Perception rolls when the character isn't being attentive, hasn't got any reason to be attentive (meaning you're always attentive while in the dungeon, obviously, but if you're in your home, or you're at a school or work place where you're comfortable, then you're not).

Normally this modifier is -2, meaning that most Humans have a Perception of 3 but a Casual Perception of only 1 (meaning fairly low odds of Casually noticing an RD 12 sniper on a roof). A few Humans, with some odd brain fault, may have a worse modifier (maybe if you're Absent-Minded it becomes -3?). You can reduce this modifier by 1 with a specific inborn Genius Trait, and by another 1 with a particular kind of training regimen (many scout/spy/investigator-type characters get this during training, or learn it on the job later). Sherlock Holmes, of course, would have both.

The Casual Perception modifier is ignored if it is zero. If not, then it applies to all Sense rolls.