The **Success roll** is based on *effective* skill rather then actual skill.

## Probability TableEdit

Because GURPS uses a bell curve it helps to understand the chances to get a certain roll.

3-4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

Single % | 1.9 | 2.8 | 4.6 | 6.9 | 9.7 | 11.6 | 12.5 | 12.5 | 11.6 | 9.7 | 6.9 | 4.6 | 2.8 | 1.4 | 0.5 |

Cumulative % | 1.9 | 4.6 | 9.3 | 16.2 | 25.9 | 37.5 | 50.0 | 62.5 | 74.1 | 83.8 | 90.7 | 95.4 | 98.1 | 99.5 | 100 |

## Critical Success and Failure TableEdit

Modified Skill Level | Critical Success | Critical Failure |
---|---|---|

2 or less | NR* | NR* |

3 | 3-4 | 13-18 |

4 | 3-4 | 14-18 |

5 | 3-4 | 15-18 |

6 | 3-4 | 16-18 |

7-14 | 3-4 | 17-18 |

15 | 3-5 | 17-18 |

16+ | 3-6 | 18 |

* If a non defense roll is attempted it is an automatic failure though the roll tells it is a normal or critical failure. For defense of 1 a critical failure is 11 and 2 is 12.

## Extended Critical TableEdit

This was an extension of the above table given in GURPS Compendium II^{[1]}

Modified Skill Level | Critical Success | Critical Failure |
---|---|---|

20-24 | 3-7 | 18 |

25-29 | 3-8 | 18 |

30-34 | 3-9 | 18 |

35+ | 3-10 | 18 |

## Additional DetailsEdit

- a critical success on an attack roll is a Critical Hit
- a critical success on an active defense results in a Critical Miss for the attacker
- A critical failure on an attack is a Critical Miss
- A successful attack is also a critical miss if an active defense critically succeeds to thwart it
- A critical failure on a parry also functions like a critical miss

- Other active defenses can also critically fail:
- A critical failure on a block unreadies the shield
- A critical failure on a dodge results in a fall

## Task DifficultyEdit

Not all skill checks are created equal and difficulty modifiers are a way to simulate this.

- Automatic: +10 or wave roll entirely
- Trivial: +8 or +9
- Very Easy: +7 or +6
- Easy: +4 or +5
- Very Favorable: +3 or +2
- Favorable: +1
- Average: no modifier
- Unfavorable: -1
- Very Unfavorable: -2 or -3
- Hard: -4 or -5
- Very Hard: -6 or -7
- Dangerous: -8 or -9
- Impossible: -10 or no success possible

Extra Time (*noncombat* actions): 2x as long gives +1, 4x gives +2, 8x gives +3, 15x gives +4, and 30x gives +5.

Haste: -1 per 10% less time taken; 90% (taking 1/10 the prescribed time) max.

## Special CasesEdit

Per http://www.sjgames.com/gurps/faq/FAQ4-3.html#SS3.1.3 all rolls are impossible if target number is below 3, but are still rolled if attempter does not realize impossibility to determine if it is a normal failure or a critical failure. A roll of 3 can be a critical failure if rolling against a -7 skill.

Exceptions are:

- defense rolls
- resistance rolls to magic or poison
- most forced IQ and HT rolls
- any other resistance roll against a force directly targeting a living or sapient being

## ReferencesEdit

- Basic Set pg 345-6

- ↑ pg 73