The mean and standard deviation (std. dev.) characterize the normal density curve. The mean is the center point of the density curve. Below, three std. dev. to the left and to the right of the mean are marked on the graph axis. To change these parameters type in the desired value(s) and press the Update button. By default the mean is set equal to 0 and the std. dev. is set equal to 1 (i.e., "Standard Normal Density").
The curve tails are delimited by the two vertical green flags. The tail values can be set by clicking on a flag and dragging. Notice that a flag's value is displayed at the top of each flag. If the 2-Tail checkbox is checked the tails are locked symmetrically around the mean.
The applet calculates the area shaded dark yellow under the curve. To find the proportion
of values less than a given value, drag the left flag to that value. Similiarly, to find
the proportion of values greater than a given value, drag the right flag to
that value. For the proportion between two values, drag the right flag to the
smaller value, and the left flag to the larger value.