Like Hi Lo graphs, Box graphs display not only a Y-value for each X-value, but a range of Y-values for a given X-Value. Box graphs are typically used to display the upper and lower variances associated with each Y value. This variance range is displayed as a rectangle. The median point can also be marked. You can even fill in the High and Low Y data ranges to combine a Hi Lo and a Box graph.
Just as with line and bar charts, Box graphs can show multiple sets of data. You can use the Data Sets dialog box to mark the Y data with into boxes, circles, etc. This will cause the median data to be marked with the same type of marker, but with a solid color. You can also use the Skew Data button in the General graph dialog to offset the data sets from each other. This helps in discriminating the data points of one data set from another. The points in each data set can also be connected with line segments or splines. You have the same flexibility in determining the look of the Box graph as you do with Hi Lo graph.