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Old 09-17-2005, 07:21 PM   #1
PK
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Default Using "Either/Or" limitations

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.
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Old 09-17-2005, 09:12 PM   #2
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Default Re: Using "Either/Or" limitations

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.
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Old 09-17-2005, 09:16 PM   #3
DryaUnda
 
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Default Re: Using "Either/Or" limitations

All that's needed now is to post this to the wiki. :)
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Old 09-17-2005, 10:26 PM   #4
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Default Re: Using "Either/Or" limitations

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.
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Old 09-18-2005, 12:50 AM   #5
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Default Re: Using "Either/Or" limitations

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

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Old 09-18-2005, 08:20 AM   #6
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Default Re: Using "Either/Or" limitations

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
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Old 09-18-2005, 11:20 AM   #7
Not another shrubbery
 
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Default Re: Using "Either/Or" limitations

Quote:
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 :)
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Old 09-18-2005, 11:22 AM   #8
PK
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Default Re: Using "Either/Or" limitations

Alternative Abilities is a different animal, though. Note that I didn't say this was for powers in which you got to choose which limitation applied; it's for powers in which either you or circumstances decide. For example, say you're building an area effect knockout gas that's pheromone-based, so only females get a resistance roll. You cannot do that with Alternative Abilities; you have to "limit the limitation" instead. (Either Resistable or Accessibility, Males Only.) And many people may not realize that you can reverse-figure the enhancement-limiting rule for this purpose.

Or let's say I was building a character with tough skin but an armored underbelly. I'd take DR with (Either Tough Skin or Vitals Only, -12%). If you'd have me buy that with Alternative Abilities, I'd have to choose each turn whether my vitals were protected fully OR whether my body was protected completely. No thanks. :)

Thanks for the comments, though -- I realize now that I used too many "active choice" examples. I'll rewrite my website version to use more passive ones to make sure the concept comes across clearer.

BTW, just in case it isn't 100% clear -- I'm not saying (A) this is some great breakthrough or (B) that I even came up with it. It's just something that I did the math on way back in 3E days and thought some people might benefit from.
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Last edited by PK; 09-18-2005 at 11:26 AM.
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Old 05-18-2016, 04:36 PM   #9
cylys_aea
 
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Default Re: Using "Either/Or" limitations

Hi,

I think in the case of either/or limitations (or enhancements for that matter) it is better to use the reciprocal of sum of reciprocals. For the example given in "POWER-UPS 8: LIMITATIONS" p.6 it should be calculated as:

1/(1/0.2+1/0.3)=1/(10/2+10/3)=1/(30/6+20/6)=1/(50/6)=6/50=12%

It gives a fairer result while always resulting in a lower value than both of the limitations in question.
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Old 05-18-2016, 05:32 PM   #10
Anthony
 
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Default Re: Using "Either/Or" limitations

Is necromancing ten year old threads really needed?
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