Converting D&D DC to GURPS Skill penalties

[Gudiomen]

Originally Posted by Rupert

Not true. Once your adjusted skill drops below three in GURPS you can't succeed either. Also, in D&D you can get good enough to always succeed (there are no auto-failure rules for skills), whereas you can't do that in GURPS.

The games have different core assumptions, but if you're not looking at the very high end (points, levels), much of the stuff converts nicely with a bit of thought.

Good point, I forgot about the 3- rule. But the possibility of allways-win or allways-loose situations is precisely my critique on the system.

I agree that it can be converted nicely, I just don't think they way to go is by direct mathematical formulas converting DC to bonus/penalties. Or probability of success for that matter. It's way better to look at it from the descriptive/subjective perspective... you'll end up with more satisfying results in GURPS, instead of imported success rates that don't "feel right".

[The Wrathchild]

Originally Posted by Gudiomen

In D&D if you can't reach that target number, it's impossible, in GURPS you can allways try...

Actually GURPS and D&D have similar concepts here. B345 says: "You may not attempt a success roll is your effective skill is less than 3.". The only exeption to this is defence rolls that always succeed on a 3-4.

So if modifiers take you below 3, no roll, similar to the DC being too high.

Not the same. Similar.

An example would be an average-bloke-untrained-pistol-shooter trying to hit something at 100 yds. Even with aiming.

[sheakauffman]

Sorry to Necro this thread, but I have actually worked out this problem.

First Average for d20 is 10, and average for Gurps is 0, since Gurps uses a "penalty shift" system.
And the average "default" penalty in Gurps is 5, which I think goes right in line with setting the base-case for Gurps at a DC 15. Which was arrived at by totally different means in the first post.

Now to get the mechanical conversion, you have to figure out the relative value of a +1, which you can figure by comparing the deviations from the means of the two systems. In the case of Gurps you have a deviation of 2.96, and in the case of d20 the deviation is 5.77. That means that you are close to a 2 to 1 value for each +1.

That means the following would more or less be equivalent penalties to DC's:

5 - +7
10 - +4
15 - 0
20 - -4
25 - -7
30 - -11
35 - -14
40 - -18

That being said, I can't remember seeing a penalty above 10 in Gurps. Gurps seems to max out at an (mechanical) equivalent of DC-30.

[Bruno]

Originally Posted by sheakauffman

That being said, I can't remember seeing a penalty above 10 in Gurps. Gurps seems to max out at an (mechanical) equivalent of DC-30.

Bwahahahaha. Hang on while I find the thread. *shuffles around in the back archives*

Here it is. Absurdly High Skill Levels

[Mailanka]

Originally Posted by sheakauffman

That being said, I can't remember seeing a penalty above 10 in Gurps. Gurps seems to max out at an (mechanical) equivalent of DC-30.

Originally Posted by Bruno

Bwahahahaha. Hang on while I find the thread. *shuffles around in the back archives*

Here it is. Absurdly High Skill Levels

Yeah. -10 is generally the single worst modifier you can have (and even that's not true: Range penalties can get worse than -10). But mods can stack. People often point to combat because they're familiar with that, but quite a few other things can have stacking mods. If you're using TL/8 surgery to stabilize a mortal wound on an elf (-2) who is at -4xHP (-4) while you have nothing but a butcher's knife and your fingers (Improvised tools at best -5, with -2 for a lack of anesthesia), on an unsanitized dining-room table (-3), and you only have 15 minutes (10% of time, -9), you're at -25.

(And that scenario might sound ridiculous, but I could actually picture an Urban Fantasy game where a severely wounded elven prince needs to be tended to by rushed, retired physician in the midst of a warzone. In fact, the scene in Walking Dead where the boy had been shot and a veterinarian needed to perform surgery on him in a bedroom with minimal tools, while a lesser version of the above, would have some pretty steep penalties too).

If you dig around enough, you can find similar penalties for other skills (Driving in near pitch-black darkness, with a damaged semi- when you've never driven this model AND you're used to TL 6 vehicles, while moving at top-speed and badly injured; investigating a murder scene in the midst of a busy street three days after the event, while drunk, with no tools except the Mk 1 eyeball, etc)

[vicky_molokh]

I once started a thread on extreme penalties to skills and the feats that come with said penalties. I'd be happy to see more examples.

[sheakauffman]

I mean we can go there if you want...

d20	Fate	Gurps
0      -3     11
5      -2     7
10     0     4
15     1     0
18     2     -2
20     3     -4
25     4     -7
28     5     -9
30     6     -11
35     7     -14
40     8     -18
42     9     -19
45     10    -21
50     11    -25
52     12    -26
55     13    -28
57     13    -30
60     14    -32
65     15    -35
67     16    -37
70     17    -39
75     18    -42
77     19    -44
80     20    -46
85     21    -49
90     22    -53
92     23    -54
95     24    -56
100    25    -60
102    26    -61
105    27    -63
110    28    -67
113    29    -69
115    30    -70
120    31    -74
125    32    -77
127    33    -79
130    34    -81
135    35    -84

[Rasputin]

Originally Posted by sheakauffman

I mean we can go there if you want...

Just go with each 2 over 15 gives you a -1 in GURPS. It's close enough, and what I use for porting traps and stuff.