Standard deviations are important here because the shape of a normal curve is determined by its mean and standard deviation. The mean tells you where the middle, highest part of the curve should go.

The normal distribution describes a symmetrical plot of data around its mean value, where the width of the curve is defined by the standard deviation. It is visually depicted as the "bell curve." ...

The applet shows how changing these two values determines the shape and spread of the distribution curve. ... This web calculator allows users to specify the mean and standard deviation (SD) of the ...

Using the empirical rule, for example, if 100 test scores are collected and used in a normal probability distribution, 68% of those test scores should fall within one standard deviation above or ...