the ends of the box are the upper and lower quartiles, so the box spans the interquartile range.the median is marked by a vertical line inside the box.the whiskers are the two lines outside the box that extend to the highest and lowest observations.The first step in constructing a box-and-whisker plot is to first find the median (Q2), the lower quartile (Q1) and the upper quartile (Q3) of a given set of data. You are now ready to find the interquartile range (IQR). ... The IQR is a very useful measurement.
