[RAW] Compendium of Sense Rolls clarifications (looking for one . . .)

[vicky_molokh]

Greetings, all!

I'm starting this thread in the hopes of assembling, by mining the books and the forum, and getting sound advice, a reasonably complete compendium of clarifications about the way Sense Rolls work, whether due to ambiguities, omissions, implicit but non-obvious bits of info etc. Replies by official sources would be nice. Whatever the case may be, I'm looking specifically for RAW answers, not houserules. If this thread gets a reasonable amount of stuff cleared, I'll link or quote it into the uFAQ.

Comprehension Rolls
Something oft-missed, it seems. Comprehension rolls make the difference between the perceptive but not very analytical mind, and the absent-minded (lowercase) genius. A Sherlock Holmes type has both Per and IQ at high

Vision
The most commonly-used sense in games, it seems. Vision mostly relies on the use of Speed/Range modifiers (aka SSRT) and the Darkness Penalties, primarily. An extremely important bit is the Plain Sight modifier, which grants a +10 to notice stuff that isn't hidden, fine detail etc. Overall, it seems to provide reasonable results out of the box. But . . .

Vision vs. Stealth and/or Camouflage. Okay, this is slightly puzzling. If someone is trying to stick to the shadows, or to use technical means to conceal oneself, it becomes a quick contest against the appropriate skill. But what happens if both things happen? Need to win two Quick Contests?
Furthermore:

Originally Posted by B222

If someone is specifically on the
alert for intruders, the GM will roll a
Quick Contest between your Stealth
and the sentinel’s Perception.

Does this mean that a Sense Roll is allowed only if the character is actively on the lookout, and otherwise an unresisted successful Stealth roll negates sense opportunities?

----
Hearing
Okay, so Hearing gives a +1/-1 per halving/doubling distance. Yes, I know this is controversial, but essentially it's half the SSRT modifier.
However, for many hearing checks, the two important questions are what is the default distance for a given noise, and what modifiers are typical. I.e.:
A Normal Conversation has a default range of 4 yards. That means a 50/50 chance of hearing a normal conversation at this distance, which seems like an extremely poor chance. Which means that maybe there's some sort of implicit TDM similar to non-stressful tasks TDM there? At least +4 seems in order, perhaps even +6, as normal conversations are held at 2-4 very commonly, with little to no losses of messages.

Stealth: Stealth is contested against Hearing, so it's important to know what distance is the default distance for the QC. The closest indication I can find is High-Tech, page 158, where 'a stalking person' is considered to be 40 dB(A) / ¼ yards range. That seems to indicate that a Stealth vs. Hearing contest at before reaching a 1-yard distance for a backstab will be rolled at -2 for Hearing. Then again, Hearing-2 is what one rolls to hear an invisible attack in combat. So maybe there is a hidden TDM for a less stressful situation?

----

Taste/Smell
Taste is mostly straightforward, but I have no idea whatsoever what modifiers smell should take (for a non-Discriminatory character). Just how hard is a 'I hate it when they come home smelling like their ex-girlfriends' roll? How good is the several-molecules-per-million sense of smell that sharks possess (yes, I know Discriminatory gives +4)?
How far can the scent of recently-shot gunpowder be detected with a Smell+0 roll? How does the modifier change from firing more than one cartridge? By type of cartridge?
(I have a dull sense of smell, so figuring those answers empirically is extra-hard for me.)

Stealth: Stealth is used at -5 against Discriminatory Smell . . . how does that interact with the range issue?
----
Scanning Sense
Scanning senses have a designated range, after which they start accumulating stacking -2 penalties per doubling. But what are the modifiers to the Sense roll within the designated range? I mean, I suppose detecting something close to the sensor should be easier to detecting it near the very edge of the designated range. +2 at point-blank? It's kinda weird to have only a 50/50 chance to detect things real close, or even a 25% chance to miss a human-sized target at point-blank with a LADAR or the like.

Stealth: seems like due to having a decent sense roll up to the designated range, Scanning Senses are a good way of negating stealth and camouflage.
----

So, any good ways to resolve those questions?
Thanks in advance!

[sir_pudding]

Originally Posted by vicky_molokh

Furthermore:
Does this mean that a Sense Roll is allowed only if the character is actively on the lookout, and otherwise an unresisted successful Stealth roll negates sense opportunities?

If you are "stealthing" past someone who is completely insensate, or uninterested, then I don't think you even need to roll.

Hearing
Okay, so Hearing gives a +1/-1 per halving/doubling distance.

GURPS Mysteries gives a completely different rule. I don't know if this was intended as a simplification, or it's another leftover 3e-ism (and therefore errata).

[vicky_molokh]

Originally Posted by sir_pudding

If you are "stealthing" past someone who is completely insensate, or uninterested, then I don't think you even need to roll.

The question is, what level of 'not specifically looking' counts as 'completely insensate or uninterested', then.

Originally Posted by sir_pudding

GURPS Mysteries gives a completely different rule. I don't know if this was intended as a simplification, or it's another leftover 3e-ism (and therefore errata).

Err, Mysteries seems like a mysterious dead-end branch of rules that eventually got overruled: Mysterious Hearing rules got overruled by High-Tech's dB(A) table, Mysterious Influences got overruled by Social Engineering, Mysterious Gear by High-Tech gear etc. I'm not sure how much this is an official stance. But it does seem to contain stuff that doesn't mesh with newer books.

[Gollum]

Originally Posted by sir_pudding

If you are "stealthing" past someone who is completely insensate, or uninterested, then I don't think you even need to roll.

The basic rules in GURPS is that you roll whenever there is a risk (When to Roll, GURPS Lite, page 2 and GURPS Basic Set, page 343).

Trying to hit a target at point blank range, for instance, requires a roll, even if the target is stationary. So, even if reason would indicate that trying to stealth someone who doesn't pay any attention to his surrounding is an utterly trivial task in reality, it is not in GURPS. It requires a roll: exactly as the target can suddenly move in the hit-at-point-blank-range situation, the attention of the victim of the stealth can suddenly be attracted by a light, a movement or a noise in the surrounding.

Now, if someone does not pay any attention to his surrounding, he obviously has a penalty for the quick contest. And this penalty can be quite high. Something like -5 if he is reading a book, for instance, -7 if he is watching TV and -10 if he is asleep... These penalties are not at all official, though (just my GM's judgment).

[David Johnston2]

Originally Posted by vicky_molokh

Comprehension Rolls
Something oft-missed, it seems. Comprehension rolls make the difference between the perceptive but not very analytical mind, and the absent-minded (lowercase) genius. A Sherlock Holmes type has both Per and IQ at high

Rolls to understand something are almost always done with IQ skill rolls. There's always some relevant skill.

\

Vision vs. Stealth and/or Camouflage. Okay, this is slightly puzzling. If someone is trying to stick to the shadows, or to use technical means to conceal oneself, it becomes a quick contest against the appropriate skill. But what happens if both things happen? Need to win two Quick Contests?

If two skills are used at the same time for the same purpose when that's possible, that's a complementary skill roll.

Furthermore:
Does this mean that a Sense Roll is allowed only if the character is actively on the lookout, and otherwise an unresisted successful Stealth roll negates sense opportunities?

Yes. If you're trying to sneak past someone who isn't watching for intruders, then they only get a perception roll if you fail your stealth roll.

----
Hearing
Okay, so Hearing gives a +1/-1 per halving/doubling distance. Yes, I know this is controversial, but essentially it's half the SSRT modifier.
However, for many hearing checks, the two important questions are what is the default distance for a given noise, and what modifiers are typical. I.e.:
A Normal Conversation has a default range of 4 yards. That means a 50/50 chance of hearing a normal conversation at this distance,

Actually a 50/50 chance of getting a complete picture of what people are saying at that range. There is a TDM if you are just trying to overhear that a conversation is going on but not what they are saying. There's also a built in assumption that there's a bit of ambient noise.

which seems like an extremely poor chance. Which means that maybe there's some sort of implicit TDM similar to non-stressful tasks TDM there? At least +4 seems in order, perhaps even +6, as normal conversations are held at 2-4 very commonly, with little to no losses of messages.

No, "norma"l conversations are not held from 12 feet away. Normal conversations take place between people in adjacent hexes or even in the same hex, creating a positive TDM. If you are talking to someone 4 hexe away, then you raise your voice a little to compensate. There should also be a TDM for having a person actually facing toward you and talking to.

Taste/Smell
Taste is mostly straightforward, but I have no idea whatsoever what modifiers smell should take (for a non-Discriminatory character). Just how hard is a 'I hate it when they come home smelling like their ex-girlfriends' roll?

Start by thinking about the TDM for people who are actually deliberately wearing perfume. That would probably be a +4 unless they over-do it. Perfume is designed to be noticed and to be persistent. Second hand perfume would depend on how much physical contact we're talking about but it would go down from there.

How good is the several-molecules-per-million sense of smell that sharks possess (yes, I know Discriminatory gives +4)?

Sharks can reputedly smell blood at a range of over two miles. They're also incredibly dumb in part because most of their not very large brains is devoted to their sense of smell. By the book they have a modified roll to do that of 16. Problem is that claim doesn't specify how much blood at the site (but dolphins contain a LOT of blood) we're talking about or the speed of the current between the injured animal and the shark. Also I suspect smelling food when you're hungry is a positive TDM.

How far can the scent of recently-shot gunpowder be detected with a Smell+0 roll?

Probably not really far. Assuming still air, a single shot and not much in the way of ambient "noise" and a modern automatic pistol you'd have to be quite close. Only a yard or so.

How does the modifier change from firing more than one cartridge? By type of cartridge?
(I have a dull sense of smell, so figuring those answers empirically is extra-hard for me.)

Stealth: Stealth is used at -5 against Discriminatory Smell . . . how does that interact with the range issue?

It's important to ask "is the air moving". I mean you can turn to Hearing as a model for smelling things in totally still air but outside the air is almost never still. Air movement basically creates a telescopic smell effect.


----

Scanning Sense
Scanning senses have a designated range, after which they start accumulating stacking -2 penalties per doubling. But what are the modifiers to the Sense roll within the designated range? I mean, I suppose detecting something close to the sensor should be easier to detecting it near the very edge of the designated range. +2 at point-blank? It's kinda weird to have only a 50/50 chance to detect things real close, or even a 25% chance to miss a human-sized target at point-blank with a LADAR or the like.

People and things with scanning sense don't generally go with a 10 perception for just that reason.

Stealth: seems like due to having a decent sense roll up to the designated range, Scanning Senses are a good way of negating stealth and camouflage.
----

Well camouflage would be useless against a scanning sense unless it was specifically designed for that sense

[Gollum]

Originally Posted by David Johnston2

Rolls to understand something are almost always done with IQ skill rolls. There's always some relevant skill.

Yes. rules are clear about that.

Comprehension Rolls: A successful Sense roll means you noticed something. That is often sufficient, but in some cases, the GM may require a second roll to understand what you have sensed; e.g., to realize that the “owl hoot” you heard is really an Indian warrior, or that the faint scent you noticed belongs to the flower of a man-eating plant. This roll is against IQ for details that anyone could figure out, or against an appropriate skill if the significance would be lost on anyone but an expert. (GURPS Lite, page 24).

Originally Posted by David Johnston2

If two skills are used at the same time for the same purpose when that's possible, that's a complementary skill roll.

I do agree. Camouflage is usually used by people who don't move while Stealth is used by moving people. Indeed, Stealth is described in the rules as the ability to "hide and to move silently." (GURPS Lite, page 17). So, it surely includes some camouflage techniques... And vice versa (Camouflage includes some Stealth techniques like taking benefit from shadows, making no noise...).

Now, if a player really insists on using both skills I would use the rules of Complementary Skills (Actions 2, page 5). After all, it makes sense.

[Gollum]

Originally Posted by David Johnston2

Actually a 50/50 chance of getting a complete picture of what people are saying at that range. There is a TDM if you are just trying to overhear that a conversation is going on but not what they are saying. There's also a built in assumption that there's a bit of ambient noise.

Yes. Just try to notice the number of times you ask someone to repeat what he just said because you didn't understand some words and don't really get what he meant...

Ordinary conversations don't require rolls in GURPS, exactly like driving into town for someone who knows how to drive, or finding the keys of your cars... In reality, we all fails such ordinary tasks regularly. Which means that if it become important for an adventure (stress, danger...), these rolls can be failed.

[sir_pudding]

Originally Posted by Gollum

Trying to hit a target at point blank range, for instance, requires a roll, even if the target is stationary. So, even if reason would indicate that trying to stealth someone who doesn't pay any attention to his surrounding is an utterly trivial task in reality, it is not in GURPS. It requires a roll: exactly as the target can suddenly move in the hit-at-point-blank-range situation, the attention of the victim of the stealth can suddenly be attracted by a light, a movement or a noise in the surrounding.

If the person is totally insensate or utterly unconcerned there is no risk, and therefore there is no reason to roll. You don't need to roll to sneak past a corpse (ordinarily) or a person who actually doesn't care if you are there or not (though the GM may call for a roll anyway if you aren't aware of what's actually going on; but failure is irrelevant). Sneaking past absolutely nobody at all, should also probably not require a roll.

Originally Posted by Gollum

Ordinary conversations don't require rolls in GURPS, exactly like driving into town for someone who knows how to drive, or finding the keys of your cars...

Yes, this is the same thing as what I'm saying.

You only need to roll Stealth versus Perception if there is a sentient creature or sensor that can detect you, and will do something as a result of detection. In which case you do need to roll it.

[Gollum]

Originally Posted by sir_pudding

If the person is totally insensate or utterly unconcerned there is no risk, and therefore there is no reason to roll. You don't need to roll to sneak past a corpse (ordinarily) or a person who actually doesn't care if you are there or not (though the GM may call for a roll anyway if you aren't aware of what's actually going on; but failure is irrelevant). Sneaking past absolutely nobody at all, should also probably not require a roll.

Yes, this is the same thing as what I'm saying.

You only need to roll Stealth versus Perception if there is a sentient creature or sensor that can detect you, and will do something as a result of detection. In which case you do need to roll it.

Yes, sorry. I didn't get the meaning of "insensate". I just believed you were talking about someone who don't really pay attention to his surrounding. Someone reading a book, watching the TV, or even sleeping... Brief, a guard who does not his job seriously for instance. Such a guy can still notice the presence of a character who tries to sneak past him... With a lot of luck!

But now that I understand your post better, I fully do agree with you.

[sir_pudding]

Originally Posted by Gollum

Yes, sorry. I didn't get the meaning of "insensate". I just believed you were talking about someone who don't really pay attention to his surrounding. Someone reading a book, watching the TV, or even sleeping... Brief, a guard who does not his job seriously for instance. Such a guy can still notice the presence of a character who tries to sneak past him... With a lot of luck!

But now that I understand your post better, I fully do agree with you.

To clarify, I mean that "specifically on the alert for intruders" makes the most sense, IMO, if you interpret it very liberally to mean "concerned with intruders and unlikely to ignore them if detected". Otherwise you get all kinds of weird puzzles with what "on the alert" actually means. If there's a sentry (even a bored one and even an accidental one), you need to roll a Contest, IMO.