Size Modifier and poison

[Donny Brook]

Originally Posted by Varyon

"Height" here is a stand in for "effective linear dimension" - a quadruped uses its length instead of its height, a somewhat-elongated sphere uses ~1.5x its longest dimension, a sphere uses ~2x its diameter, etc. If you are maintaining the same basic shape, the function would indeed be linear with height (and pretty much any other linear measurement on the target).

Are you saying poison/drug dosages in real life are linear with what GURPS calls SM? That is, the appropriate dosage for an SM+3 elephant is around three times that for an SM+0 human? Because that's how the GURPS poison rules work, and that seems rather off to me (but then, I'm nowhere near an expert on the subject).

I'm not going so far as to comment on the correct dosage by size. I'm just pointing out that the SM scale is not linear in terms of change-in-length per change-in-modifier.

[Anders]

I was going for a simple rule, though. Realistically the dose scales as M^0.67 (IIRC), but that's just complicated.

[Anthony]

Originally Posted by Anders

I was going for a simple rule, though. Realistically the dose scales as M^0.67 (IIRC), but that's just complicated.

Realistically doses of poisons are generally assumed linear in mass, doses are usually listed per kilogram.

[Varyon]

Originally Posted by Donny Brook

I'm not going so far as to comment on the correct dosage by size. I'm just pointing out that the SM scale is not linear in terms of change-in-length per change-in-modifier.

I don't see how that has any bearing on the discussion? To be clear, the reason I'm saying that using the SM as a straight modifier results in a linear relationship is because +2 SM means roughly twice the linear dimension and twice the HP, and using twice as much poison as a nominal dose does twice the damage and gives a -2 to resist. That is, a poison that is HT-3 to resist and does 1d tox has a ~84% chance to do an average of 35% HP injury to a target with SM+0, HP 10, and HT 10. Doubling the dosage makes the poison HT-5 to resist and deal 2d tox, and doubling the target's height (provided they are scaled up proportionally) will make said target SM+2, HP 20, and HT 10 (effective HT 12 to resist poisons, thanks to the high SM) - so the poison will have a ~84% to do an average of 35% HP injury to the target. Thus, dosage to get the same effectiveness scales linearly with height (or, rather, effective linear dimension).

[Rolando]

SM+2 equates ain increase of roughly 2.5 in linear dimension.
And SM+3 is 3.5 increase...

That is what Donny Brook is meaning with the "it's not linear", because size modifier in GURPS is not linear with the increase of dimension.

[Varyon]

Originally Posted by Rolando

SM+2 equates ain increase of roughly 2.5 in linear dimension.
And SM+3 is 3.5 increase...

Depends on where you are in the sequence. 0.5->1, 1->2, and 1.5->3 are all x2; meanwhile 0.7-1.5 is ~x2.15, 2->5 is x2.5, and 3->7 is ~x2.33. Similarly, 0.5->1.5 and 1->3 are both x3; meanwhile 0.7->2 is ~x2.86, 1.5->5 and 3->10 are ~x3.33, and 2->7 is x3.5. It's a logarithmic function that got rounded off to readily-usable numbers, so there's no constant multiplier, but x1.5 for +1, x2 for +2, x3 for +3, x5 for +4, and x7 for +5 generally work out fine (x10 for +6 also works, but then it's always the case, there isn't any variability there since that's how SSR is defined).

[Donny Brook]

Originally Posted by Varyon

I don't see how that has any bearing on the discussion?

You said that using SM as the dosage modifier it means it scales linearly with height. But that can't be right since SM does not scale linearly with height.

[Anthony]

A realistic treatment of SM vs single target poisons would probably wind up being something like a modifier of 5xrelative SM, so against a target 2 SM larger than designed you probably don't do anything at all, against a target 2 SM smaller they just die. Against area poisons, other than increasing onset time (which is already RAW), it's not going to make much difference.

[Ulzgoroth]

Originally Posted by Varyon

I don't see how that has any bearing on the discussion? To be clear, the reason I'm saying that using the SM as a straight modifier results in a linear relationship is because +2 SM means roughly twice the linear dimension and twice the HP, and using twice as much poison as a nominal dose does twice the damage and gives a -2 to resist. That is, a poison that is HT-3 to resist and does 1d tox has a ~84% chance to do an average of 35% HP injury to a target with SM+0, HP 10, and HT 10. Doubling the dosage makes the poison HT-5 to resist and deal 2d tox, and doubling the target's height (provided they are scaled up proportionally) will make said target SM+2, HP 20, and HT 10 (effective HT 12 to resist poisons, thanks to the high SM) - so the poison will have a ~84% to do an average of 35% HP injury to the target. Thus, dosage to get the same effectiveness scales linearly with height (or, rather, effective linear dimension).

Why does that seem like a good thing, though? That's definitely the wrong outcome.

Originally Posted by Anthony

Realistically doses of poisons are generally assumed linear in mass, doses are usually listed per kilogram.

I suspect a passable model in many cases is 'what concentration will this reach in the target tissue'.

[Varyon]

Originally Posted by Donny Brook

You said that using SM as the dosage modifier it means it scales linearly with height. But that can't be right since SM does not scale linearly with height.

I'm saying it means dosage scales linearly with height. +2 to resist for being double height is countered by -2 to resist for using double dosage. I don't think I can explain it any better than this, so consider this my last attempt to do so.

Originally Posted by Ulzgoroth

Why does that seem like a good thing, though? That's definitely the wrong outcome.

I don't think it is a good thing, I was simply noting this is the result of the suggestion. It's probably more appropriate to scale dosage with the nominal body weight for your SM. So to match the effects of one dose on SM+0, you need 3 doses for SM+1, 10 doses for SM+2, 30 doses for SM+3, etc. Overdosing results in reduced time of onset and time between cycles, additional damage (probably both of these scaling linearly with dosage for simplicity - but proper dosage for your SM scales based on the nominal HP for your SM*), and a penalty to HT that scales via SSR (-1 for 1.5 doses, -2 for 2 doses, -3 for 3 doses, -4 for 5 doses, etc). Underdosing is the opposite - longer time before onset and between cycles, reduced damage, and a bonus to resist that scales with SSR.

*So divide the damage it does to SM+0 by 10, then multiply by 15 for SM+1, 7 for SM-1, etc. That gives you the damage for a proper dose at your size; using half of this cuts that damage in half, using double this doubles the damage, and so forth.