This lecture is brought to you by the Dean of Criminal Rehabilitation & Eradication

Many challenges are listed as 'Broad'. This means the probability of success increases linearly from 0 and up, with a roof on 100%. This is different from the previous system, 'Narrow', where the challenge only increased around +/- 5 levels from the challenge level.

The probability of success for a 'Broad' challenge relies on three things: the Level of the Attribute or Quality being tested, the Difficulty Level, and the Difficulty Scaler, as follows:

Probability of success = (Scaler) * (Quality Level) / (Difficulty Level). [rounded down]

### Probability Calculator

```s
template = Template:Calculator/Probability
form = Probability
result = ProbabilityResult
param = quality|Quality Level||int|0-1000
param = diff|Difficulty Level|50|int|1-1000
param = scaler|Difficulty Scaler (%)|60|int|1-100
```

The difficulty scaler for Fallen London is 0.60 (as of 9th Sept. 2013). This gives the 'base' probability of success (60%), which occurs when the Quality Level equals the Difficulty Level.

The following adjectives are used to describe the difficulty of a particular challenge, based on the calculated probability:

• 0-10%: almost impossible
• 11-30%: high-risk
• 31-40%: tough
• 41-50%: very chancy
• 51-60%: chancy
• 61-70%: modest
• 71-80%: very modest
• 81-90%: low-risk
• 91-100%: straightforward

e.g. a Broad challenge on Shadowy with a difficulty level of 50 would currently have the following chances of success:

• 0-8: almost impossible
• 9-25: high-risk
• 26-33: tough
• 34-41: very chancy
• 42-50: chancy
• 51-59: modest
• 60-67: very modest
• 68-75: low-risk
• 76+: straightforward

The Beginner's Guide's section on Change Points has information about expected earnings of the challenge attribute (at least for main attributes) per attempt at the various difficulty levels, from 1.0 at “straightforward” to 4.2 at “almost impossible”.

For further reading, this Story Nexus reference describes this rather less drily.

## More Calculators

### Difficulty Level

Work out the likely difficulty level, given your probability and quality level:

``` template = Template:Calculator/Difficulty Level
form = Difficulty
result = DifficultyResult
param = quality|Quality Level||int|0-999
param = prob|Success Probability (%)|50|int|0-100
param = scaler|Difficulty Scaler (%)|60|int|1-100
```

### Relative Probability

Given your current probability of success, what quality level will you need to achieve your desired probability?

``` template = Template:Calculator/Relative Probability
form = RelProbability
result = RelProbabilityResult
param = quality|Quality Level||int|1-999
param = prob|Success Probability (%)||int|1-100
param = prob2|Desired Probability (%)|80|int|1-100
```
``` template = Template:Calculator/ChallengeList