I though you all might be interested in this. I wrote a program to randomly roll the dice in the way described in the book and examine the probability of success in each case.

"Plus X" = number of positive dice being rolled

"Minus X" = number of negative dice being rolled

"Target = X" = Target number to roll (this number or less)

I also included a table for the average amount of stress given a number of positive and negative dice.

2 possible issues:

1) I may have misunderstood the dice rolling rules. I wrote the program today after reading the book yesterday, and I loaned my book to a roommate, so I can't check the rules.

2) These numbers are not from rigorous mathematical calculation, they are from iterating the dice rolling 10,000 times for each situation. Given Poisson statistics, they should not be more than 1% off, though.

Sorry for the terrible formatting. I hope the tables are legible.

Success Probability
Plus 2 Plus 3 Plus 4 Plus 5 Plus 6
Target = 1
Minus 0 31.10 42.37 52.40 59.87 66.93
Minus 1 25.82 36.80 45.14 53.27 60.33
Minus 2 22.36 31.83 40.33 47.66 54.75
Minus 3 19.32 27.82 35.67 43.22 49.65
Minus 4 16.04 24.47 32.42 38.80 45.59
Target = 2
Minus 0 55.76 70.68 80.70 86.62 91.03
Minus 1 48.70 63.30 73.58 81.11 86.87
Minus 2 42.22 56.35 67.41 75.02 82.34
Minus 3 36.26 49.89 61.15 70.31 77.69
Minus 4 31.03 43.97 55.94 66.00 73.96
Target = 3
Minus 0 75.35 87.60 93.86 96.79 98.48
Minus 1 67.62 81.28 89.73 94.42 96.81
Minus 2 59.04 74.71 84.23 90.80 94.55
Minus 3 51.09 67.55 79.71 86.71 91.89
Minus 4 46.22 62.48 74.69 83.28 89.47
Target = 4
Minus 0 89.27 96.60 98.92 99.63 99.83
Minus 1 81.46 93.02 97.08 99.12 99.65
Minus 2 73.74 87.66 94.59 97.93 99.24
Minus 3 65.72 82.50 91.00 95.96 98.30
Minus 4 58.13 75.44 87.44 93.80 96.55
Target = 5
Minus 0 97.44 99.58 99.93 99.97 100.00
Minus 1 93.26 98.47 99.76 99.96 99.98
Minus 2 85.79 96.06 99.05 99.73 99.94
Minus 3 77.47 91.64 97.60 99.19 99.79
Minus 4 68.99 86.57 95.13 98.00 99.58

Number of Stresses
Plus 2 Plus 3 Plus 4 Plus 5 Plus 6
Minus 0 0 0 0 0 0
Minus 1 0.6911 0.5797 0.4858 0.3976 0.3399
Minus 2 1.3831 1.1508 0.9598 0.8135 0.6786
Minus 3 2.0795 1.7319 1.4477 1.2009 1.0095
Minus 4 2.7582 2.3075 1.9263 1.6126 1.3485

This is cool!

Yes, thanks for this. Great work. I think studying these will help me calibrate how I add negative dice to checks.

Did you read the rules again? Are the formulas accurate?

Adding negative dice is as simple as adding positive dice.

Not difficult, no environmental issues = 0 negative dice

Then build up from there on a 1 for 1 basis.

You are trying to pick a new lock (-) in the dark (-) with shoddy tools not meant for the job (-) and a horrifying zombie is stalking you and will attack if you don't get the door open (-)

Easy.