Expression testing will not directly tell you the probabilities for given expressions (because this could become computationally... absurd), instead
Monte Carlo sampling is used.
That is to say, the statistics displayed are the outcomes of many (MANY) pseudorandom simulated rolls of the dice.
The default number of samples taken is 5000 and should give a good approximation of what the probabilities are for most dice expressions, however it is worth noting the limitations of this approach:
- More samples will more accurately represent the expresion's probabilities
- Expressions with very unlikely outcomes might not be represented at all. (if an outcome has a true 1/1,000,000 liklihood, there is a good chance it won't happen with only the default 5000 samples)
The number of samples is displayed in the top-right, and the process of sampling can be paused or resumed by pressing it.
To change the maximum number of samples, see the
Target Samples setting.