Advantage/Disadvantage Modifier Stacking

[BunBuJin]

My apologies if there already abounds a wealth of information on this topic as I suspect— however I’ve scoured the internet and searched in every manner of terms I can think of on this forum for the answers to my questions, and have been as yet unsuccessful in finding anything which actually answers what I’m asking.

How *exactly* are we meant to resolve a host of advantage or disadvantage modifiers as they stack multiply to an advantage or disadvantage. I’ve gone about this in multiple ways, and no matter how I do it there. Seem to be considerable “breaks” in the game balance of the process.

I spent basically all the time I have right now just searching independently for my answer and writing up to this point, so i’ll have to post more details later, but here’s the gist of what I mean:

Take purchasing DR for example. It’s easily possible to get more than -100% in modifiers, while also adding a positive value of advantageous modifiers, and end up with a net -100% cost— at which point you could have any anount of the DR which— while limited— would still function in *some* circumstances at no cost.

I’ve also searched the core books for this information and haven’t been able to locate it. Please help! Thank you!

[Celjabba]

Hello and welcome !

Limitations can never lower the price below 20% of the base price. So, anything below -80% in total modifiers is lost.

Basic p101 bottom of third column and p110, top of first column

Originally Posted by characters p101

Modifiers can never reduce cost by more than 80%. Treat a net modifier of
-80% or worse as -80%. Thus, no matter how many limitations you take, you
cannot lower the cost of a trait to less than 1/5 its base cost.

Take for exemple Damage Resistance ( 5/level )
Modifying it with some random modifiers :
Forcefield +20%
Directional (back only) -40% , Limited use - 1/day -40% , Accessibility - Only in direct sunlight -30% , Cost 2fp/use -10%

Adding all the modifiers : 20% + (-40%) + (-40%) + (-30%) + (-10%)
= 20% + (-120%) : -100% (net modifier)

>>>> changed to -80% per the rule above.

Final result is DR (various modifiers -80% : 1/lvl )
The 'excess' -20% are lost.
You could either buy more enhancement (hardened, for exemple), or drop some limitations.

Hope this help.

--------------
Note : As an optional rule (in Powers, p 102) you can use multiplicative modifiers.
The -80% rule max for limitations still apply !
In this case : 5 * 1.20 (sum of all positive modifiers) * 0.2 (sum of all negative modifiers, max -80%) , final cost 1.2/lvl
The result is arguably more fair with large enhancements (since the modifiers apply to the total cost, not just the base cost) but you will need GM calls for adjusting some enhancements and (especially) limitations values.

Note 2 : When googl-ing for answers on the forums, add "site:forums.sjgames.com" (without the quotes) to your google search.

Or you can use the forum advanced search, and search for Posts Made By Kromm or PK (Kromm is the Gurps line editor, the author of Gurps 4e, DFRPG and many supplements and general Gurps Guru. PK is another author and was assistant editor.) Both answer(ed) all kind of rules questions on the forums.

[Varyon]

While not RAW, I feel it might not be horrible to allow Limitations in excess of -80% to be combined additively with Enhancements prior to applying Multiplicative Modifiers (so if you had +50% worth of Enhancements and -100% worth of Limitations, this becomes +30% of Enhancements and -80% of Limitations, so it's 1.3*0.2=26% rather than 1.5*0.2=30%).

Also, definitely not RAW, but there are some cases where other Advantages aren't dissimilar to Enhancements, in which case I feel the points "lost" from cutting off Limitations beyond -80% could give a discount to said Advantage, although it only works when the primary power is working (and you don't get any further discount for this fact). So, if you had -90% worth of Limitations on Flight, that would normally save you 36 points. The -80% cap means you only save 32 points, but I'd let you put those "lost" 4 points toward buying Enhanced Move (Flight).

[Celjabba]

Originally Posted by Varyon

While not RAW, I feel it might not be horrible to allow Limitations in excess of -80% to be combined additively with Enhancements prior to applying Multiplicative Modifiers (so if you had +50% worth of Enhancements and -100% worth of Limitations, this becomes +30% of Enhancements and -80% of Limitations, so it's 1.3*0.2=26% rather than 1.5*0.2=30%).

That's an nice solution.

The graph give a sharp decrease in cost until you reach 80% of limitations , and then a much flater decrease as you slowly reduce the enhancements to 0...
Elegant. I will have to think, but I will probably adopt this.
Do you use it ? any edge case ?

[Varyon]

Originally Posted by Celjabba

Elegant. I will have to think, but I will probably adopt this.
Do you use it ? any edge case ?

I should note here my GURPS experience is pretty much purely from a theoretical perspective - I like to build things, but don't really have a group to play with. I can't really think of any particular edge case that could crop up. Honestly, this is arguably an edge case avoidance measure - the point of Multiplicative Modifiers is to reduce the cost of abilities that are highly-limited but have a lot of Enhancements, and this system avoids cases where Multiplicative Modifiers would actually increase the cost of something relative to the default (such as with your DR example).

[BunBuJin]

Thank you all for your responses-- I ran into more complicated issues even considering the -80% cap, but I'll have to address those at a later time when I can name them specifically. Suffice it to say for now, the system seems to break down easily during perfectly innocent attempts to capture a concept developed entirely independent of any point-buy system.

(In other words, without deliberately min-maxing!)

Cheers, and thanks again!