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Old 09-22-2014, 01:26 PM   #1
vicky_molokh
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Default [RAW] Compendium of Sense Rolls clarifications (looking for one . . .)

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:
Quote:
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!
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Old 09-22-2014, 01:39 PM   #2
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Default Re: [RAW] Compendium of Sense Rolls clarifications (looking for one . . .)

Quote:
Originally Posted by vicky_molokh View Post
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.

Quote:
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).
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Old 09-22-2014, 11:03 PM   #3
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Default Re: [RAW] Compendium of Sense Rolls clarifications (looking for one . . .)

Quote:
Originally Posted by vicky_molokh View Post
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.

\
Quote:
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.

Quote:
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.



Quote:
----
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.

Quote:
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.


Quote:
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.

Quote:
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.

Quote:
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.

Quote:
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.


----
Quote:
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.

Quote:
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
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Old 09-23-2014, 07:59 AM   #4
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Default Re: [RAW] Compendium of Sense Rolls clarifications (looking for one . . .)

Quote:
Originally Posted by sir_pudding View Post
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.

Quote:
Originally Posted by sir_pudding View Post
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.
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Old 09-23-2014, 08:38 AM   #5
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Default Re: [RAW] Compendium of Sense Rolls clarifications (looking for one . . .)

Quote:
Originally Posted by sir_pudding View Post
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).

Last edited by Gollum; 09-23-2014 at 08:42 AM.
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Old 09-23-2014, 08:58 AM   #6
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Default Re: [RAW] Compendium of Sense Rolls clarifications (looking for one . . .)

Quote:
Originally Posted by David Johnston2 View Post
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).
Quote:
Originally Posted by David Johnston2 View Post
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.
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Old 09-23-2014, 09:07 AM   #7
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Default Re: [RAW] Compendium of Sense Rolls clarifications (looking for one . . .)

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Originally Posted by David Johnston2 View Post
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.
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Old 09-23-2014, 09:15 AM   #8
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Default Re: [RAW] Compendium of Sense Rolls clarifications (looking for one . . .)

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Originally Posted by David Johnston2 View Post
No, "normal" 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.
Normal conversation don't require any roll in GURPS, exactly as driving into town (which is still dangerous in reality).

Now, in the middle of a battle where the Sergent tells his soldiers "Turn around them to the left!" only once, hearing rolls for the soldiers may be required...
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Old 09-24-2014, 05:16 AM   #9
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Default Re: [RAW] Compendium of Sense Rolls clarifications (looking for one . . .)

Quote:
Originally Posted by David Johnston2 View Post
Rolls to understand something are almost always done with IQ skill rolls. There's always some relevant skill.
Yes.
Quote:
Originally Posted by David Johnston2 View Post
If two skills are used at the same time for the same purpose when that's possible, that's a complementary skill roll.
Camouflage says that it doesn't provide a bonus to Stealth, which is why the solution seems to be inapplicable.

Quote:
Originally Posted by David Johnston2 View Post
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.
This tends to result in weird things like sneaking right next to a character with Stealth 16 almost each and every time, no matter how perceptive said character, as long as said character isn't deliberately standing guard. Which is why the question.

Quote:
Originally Posted by David Johnston2 View Post
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.
That's actually an interesting question - about those TDMs. Hear that there is a conversation seems to be what the Per roll is about, making out the contents seems to be the aforementioned Comprehension Roll (IQ-based one). TDMs for either are unclear and unmentioned in Basic Set.

Quote:
Originally Posted by David Johnston2 View Post
No, "normal" 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.
The distance from me to a colleague I tend to talk to is about 4 yards. We don't seem to be raising our voices. Occasionally we talk without taking off headphones nor turning off the music (admittedly, this is only when the music is quiet). Some interesting benchmarks for TDMs, it seems.

Quote:
Originally Posted by David Johnston2 View Post
People and things with scanning sense don't generally go with a 10 perception for just that reason.
Well, things with Scanning Sense tend to have about 12 in Electronics Operation instead of using Perception. Better sensors are usually represented with a greater designated range.
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Old 09-24-2014, 06:11 AM   #10
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Default Re: [RAW] Compendium of Sense Rolls clarifications (looking for one . . .)

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Yes.
Camouflage says that it doesn't provide a bonus to Stealth, which is why the solution seems to be inapplicable.
In which case the two skills are considered as separate. Stealth for hiding while moving (and, maybe, hiding without trying to mingle your colors in the surrounding) and Camouflage for true camouflage situations (with modifying your clothes, color, and so on, in order to "disappear" in the setting).

Quote:
Originally Posted by vicky_molokh View Post
This tends to result in weird things like sneaking right next to a character with Stealth 16 almost each and every time, no matter how perceptive said character, as long as said character isn't deliberately standing guard. Which is why the question.
So, the Quick Contest with a penalty sounds to be the best solution when the victim of the stealth doesn't pay attention to his surrounding.

Quote:
Originally Posted by vicky_molokh View Post
TDMs for either are unclear and unmentioned in Basic Set.
Maybe because to many factors are involved. The wind, for instance, tremendously change the noise you can here. When I am at home, in my garden, for instance, I sometimes hear a train passing 3 kilometers away. But if there is no wind, I don't hear it at all.

Quote:
Originally Posted by vicky_molokh View Post
The distance from me to a colleague I tend to talk to is about 4 yards. We don't seem to be raising our voices. Occasionally we talk without taking off headphones nor turning off the music (admittedly, this is only when the music is quiet). Some interesting benchmarks for TDMs, it seems.
And don't forget the very basic rule: mundane tasks made in ordinary nonadventuring situation don't require any roll. If you didn't hear what your friend said, you just ask him to repeat.
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