You Can Do Better Than That (MOS Improvement via Luck)

[martinl]

In Jovus' game tonight, my PC (Ilsildel) will most likely throw a mass sleep spell in a situation where failure would be Bad. Ilsildel has luck, and I've been pondering what my threshold for invoking it to make the MOS as overwhelming as possible is.

This page has some nice numbers (they match mine, so they must be good) for what the odds are, but it doesn't explicitly break out how much MOS calling for the two additional luck rolls will buy you. I worked that out, and decided to share.

The table below shows how much extra MOS, on average, invoking luck will get you, after you have made the initial roll.

Init.   MOS     ExRoll
Roll    Imp.
3	0.0	3.0
4	0.0	4.0
5	0.0	5.0
6	0.1	5.9
7	0.3	6.7
8	0.6	7.4
9	1.1	7.9
10	1.7	8.3
11	2.4	8.6
12	3.3	8.7
13	4.2	8.8
14	5.2	8.8
15	6.2	8.8
16	7.2	8.8
17	8.2	8.8
18	9.2	8.8

Nothing in there is really surprising, but it gives a rough cut off for "Will invoking Luck significantly improve things?" as an original roll 9+, with significant fuzziness.

Um, I guess that's all. Hey, I tagged it with 'math wankery.'

[ericthered]

and showing that GURPS luck is about not failing, not about critical successes!

[Anthony]

The chance to improve your roll is 1 - (chance to roll your current roll or higher on 3d6)^2 -- i.e. if you roll a 9, the odds of rolling 9+ on 3d6 is 160/216, squared that is 0.549, so you've got a 44.1% chance to improve your roll. You can apply that to any other value; to roll 7- is equivalent to beating an 8, or 181/216, for a total 29.8% chance of getting a 7 or lower.

[Silvermane]

It also depends on what the individual dice roll.

If you get two 1s and a 6, it's possible that you could improve that roll(I'd use it if a critical success was something I wanted!). If you get two 4s and a 5. That's a pretty bad roll, and Luck isn't going to help you much there either. Best case scenario it turns the 5 into a one.

It's not something you can easily graph and calculate.

[roguebfl]

Originally Posted by Silvermane

It also depends on what the individual dice roll.

If you get two 1s and a 6, it's possible that you could improve that roll(I'd use it if a critical success was something I wanted!). If you get two 4s and a 5. That's a pretty bad roll, and Luck isn't going to help you much there either. Best case scenario it turns the 5 into a one.

It's not something you can easily graph and calculate.

um the luck reroll is not individual dice but complete sets of 3d6, so it doesn;t matter what the combination was just it's total.

you don't get to keep those two 1s you got to reroll them too.

[Silvermane]

Originally Posted by roguebfl

um the luck reroll is not individual dice but complete sets of 3d6, so it doesn;t matter what the combination was just it's total.

you don't get to keep those two 1s you got to reroll them too.

Originally Posted by B66

Once per hour of play, you
may reroll a single bad die roll twice
and take the best of the three rolls!

'Single bad die' seems to imply to me that you take one of the bad die and re-roll it... It's how I've been playing it. o.o

I'm not sure if this is worse or better than re-rolling all three.

[roguebfl]

Originally Posted by Silvermane

'Single bad die' seems to imply to me that you take one of the bad die and re-roll it... It's how I've been playing it. o.o

I'm not sure if this is worse or better than re-rolling all three.

except in GURPS rule mean the roll total is what it means by a die role. so a 3d6 skill check is a single die roll in its totality.

[vierasmarius]

Originally Posted by Silvermane

'Single bad die' seems to imply to me that you take one of the bad die and re-roll it... It's how I've been playing it. o.o

It's "single bad die roll", ie the entire set of three dice.

I'm not sure if this is worse or better than re-rolling all three.

In most cases it'll be worse, since (as you note) if all three dice of the original roll are poor you won't be able to improve it much. It's only in cases where a single die of the roll is undesired that this will be better than normal. It could make for an interesting limitation or lower-powered variant to Luck.

[Anthony]

Originally Posted by Silvermane

I'm not sure if this is worse or better than re-rolling all three.

It's more predictable, which is probably better, but I'm not sure how its average compare. In any case, that's not the way the rules are intended to work.

[Silvermane]

Originally Posted by vierasmarius

In most cases it'll be worse, since (as you note) if all three dice of the original roll are poor you won't be able to improve it much. It's only in cases where a single die of the roll is undesired that this will be better than normal. It could make for an interesting limitation or lower-powered variant to Luck.

Personally in my Campaigns, I might just make it work like that by default and have a second version of luck that's higher priced.

I've always thought that re-rolling at will is REALLY powerful and 15 points feels kind of cheap to me. Even if it is only once per hour.

I'll just make it a house rule instead of a bad interpretation.