Standard normal distribution

The standard normal distribution is a normal curve with mean $\mu = 0$ (mu) and standard deviation $\sigma = 1$ (sigma). Any normal value converts to it through the z-score $z = \frac{x - \mu}{\sigma}$, which rescales the data onto this common curve. For example, a value 2 standard deviations above its mean maps to $z = 2$ on the standard normal. A z-table or calculator then gives the area, and therefore the probability, to the left of that z-score.