Using "Either/Or" limitations

[PK]

Normally I don't post it when I update my site, but I think this might be helpful for a lot of people -- especially those who, unlike me, spend their evenings doing something besides playing around with the calculations in GURPS to see if there's a better way to do something. :)

USING "EITHER/OR" LIMITATIONS

Some concepts call for an "either/or" limitation. For example, a super's Innate Attack may only have a 50-yard range unless they spend two Fatigue Points (either Reduced Range x1/2 or Costs Fatigue, 2 FP). Or the use of one's Luck may have to be declared in advance for everything except defensive rolls (either Active or Defensive). The rules do make these combinations possible, though it isn't immediately obvious that they're supported, much less how to implement them.

Let me first share the simple rule, then go on to explain why it works and why it isn't a new rule, but something drawn directly from Characters. That way, anyone who doesn't care about how we got there can move on:

When an ability is designed so it can be affected by either one limitation or an alternate limitation, multiply the percentage values of both limitations together to arrive at a final value.

For example, a Jumper always arrives naked unless he spends an extra 10 minutes visualizing his gear (up to BL) coming with him. He thus has "Either Naked (-30%) or Preparation Required, 10 minutes (-30%)" as an either/or limitation. He multiplies the two together (0.30 x 0.30), for a final value of -9%. His ability is much more versatile than if he'd taken either of those limitations by themselves, and the value reflects that.

If either limitation somehow exceeds -80%, reduce it to -80% for this calculation.

Anyone who's read the box on Fantasy, p. 130 ("Behind the Curtain: Cost of Divided and Restructurable Magery") has seen a glimpse of this already, albeit a rather complicated one. It's just an upside-down way of implementing the optional "Limited Enhancements" rule in the box on p. B111. If a power has a limitation worth -X%, then you could think of not having that limitation as a +X% enhancement. You then limit the enhancement (with the second limitation).

Let's take the Jumper example. Since it's 100 points, it makes the percentages really easy to follow. Jumper (Naked, -30%) costs 70 points. Not arriving naked every time is effective a +30% enhancement (cancelling out the limitation). So, using the "Limited Enhancements" rule, we apply the Preparation Required, 10 minutes (-30%) to the +30% "Not Naked" enhancement, making it a +21% net enhancement. So now we have Jumper (Naked, -30%; Not Naked but Preparation Required, 10 minutes, +21%) [91]. Obviously, it's simpler to combine the two modifiers into a simpler form, as Jumper (Either Naked or Preparation Required, 10 minutes, -9%) [91]. Since the math works out the same every time (math is good like that), we can just use the simpler method of multiplying the two instead.

The "-80% rule" is just a rewording of the rule that a "Limited Enhancement" cannot be reduced below 1/5 of its normal value. Since each limitation can be seen as limiting the other, neither one can be greater than -80% for the purpose of this rule. Since there are no official limitations greater than this (and likely never will be), it shouldn't come up much.

[The Benj]

Heh. And here was me thinking this was going to be a question on the topic, so I was ready to tell you that this was how to do it.

All is well. Carry on.

[DryaUnda]

All that's needed now is to post this to the wiki. :)

[vitruvian]

Of course, if the modified cost of the two 'versions' of an ability are the same or comparable, and the Alternative Abilities rule is being used, you can just take the full limitation value on each version and never pay more than an effective +20% premium for each additional option.

For the example given of two -30% limitations, this would only save you 1% over the way presented, but for larger limitation values, it could add up.

[Gef]

Speaking of which, why isn't an alternate Alternate Form only 3 points instead of 15?

GEF

[Der Wanderer]

As much as I like the idea its only worth considering if the limitations are round -20% or smaller, so it has a very limited use...

Both Limitations are -10%
.1 x .1 = .01 equals 99% to pay
possibly better to drop both limitations... alternative power costs 108%

Both Limitations are at -20%
.2 x .2 = .04 equals 96% to pay
as alternative power
.8 + .8 x .2 = .96 equals 96% to pay
Equilibrium, both ways cost the same...

Both Limitations are -30%:
.3 x .3 = .9 equals 91% to pay
as alternative power:
.7 + .7 x .2 = .84 or 84% to pay
Alternative power model is 5% cheaper

[Not another shrubbery]

Originally Posted by Gef

Speaking of which, why isn't an alternate Alternate Form only 3 points instead of 15?

Because they're not Alternative Attacks.

Please report to the Munchkin Reeducation Chamber. Thank you.

Kidding :)

[Curmudgeon]

Originally Posted by PK

<snip>
Let's take the Jumper example. Since it's 100 points, it makes the percentages really easy to follow. Jumper (Naked, -30%) costs 70 points. Not arriving naked every time is effective a +30% enhancement (cancelling out the limitation).
<snip>

This has been bothering me for a long time and this is my first chance to post about it while the matter is somewhat current.

Reversing -30% to +30% is mathematically simple, but I don't think it yields the proper results.

If arriving naked every time is a -30% limitation on a 100 point advantage, it yields a 70 point advantage. Therefore, its value as an enhancement should yield the opposite result. That is, if arriving naked every time was the norm for a 70 point advantage, then not arriving naked as an enhancement should yield a 100 point advantage where the character doesn't arrive naked.

If we follow this as a +30% enhancement, we get (70 x 130% = 80 + 21 =) 91 points, rather than 100 points.

To go to 100 points from 70 points requires that the enhancement be valued as +42.86% or +43%. It's not particularly neat, but you could round it off to +40% or +45% if you don't mind being out about 2 points either side of 100.

[RyanW]

Originally Posted by Curmudgeon

This has been bothering me for a long time and this is my first chance to post about it while the matter is somewhat current.

Reversing -30% to +30% is mathematically simple, but I don't think it yields the proper results.

It does when you are adding up enhancements and limitations. Remember that you always add together all enhancement and limitation values before applying them as a modifier (unless you are using the multiplicative modifiers option on Powers p.102).

[PK]

Originally Posted by Hellboy

You could get that with leveled/variable limitations though, like Costs Fatigue 11 (B111) or Resistible HT+11 (B115) or Takes Extra Time 9 (same).

Power Ups 8 page 11's Backlash also unlocks a lot of options via reversed Affliction enhancements, especially if you can't resist them. Incapacitation: Unconsciousness would be -200% for example, and Attribute Penalty could give you unlimited amounts if you took a big enough hit. -10 DX would be -100%

PU8p12's Costs Hit Points 9 would give -90%

I'm not sure why you're listing all of the ways that a limitation can exceed -80%, because all of that is immaterial. In all cases, if either limitation exceeds -80%, you reduce it to -80%. Period.

How to deal with this is also a problem when it comes to more than just 2 limitations. Like "(A and B) or (C)". For small amounts I'd probably treat the summed limitations as a single limit, but that also creates more ways to reach past 80%.

Not really; you'd just multiply all three together. Though frankly, at that point I'd probably just call it a special effect or, at worse, a quirk. "I have three limitations, but only the least-bad one applies in every situation" is hardly a limitation at all unless all of them are pretty massive.