Normal Distribution

The normal distribution, the familiar bell curve, clusters values around an average with an equal spread above and below. Most samples land near the mean and fewer land far from it.

Write N(mean, sd), or Normal(mean, sd), where sd is the standard deviation:

N(10, 2)

centres on 10 with most values within a few units either side. Use it for a measurement that varies symmetrically around a target, such as a machine cycle time. Because a time can never be negative, any draw below zero is clamped to 0; if your mean is close to zero this distorts the result, so prefer a lognormal for short, right-skewed times.