A Histogram is a graphical display of data using bars of different heights. It is used to summarize discrete or continuous data that are measured on an interval scale. It is an estimate of the probability distribution of a continuous variable and was first introduced by Karl Pearson. It consists of tabular frequencies, shown as adjacent rectangles, with an area equal to the frequency of the observations in the interval and groups numbers into ranges and is one of the basic quality tools. When the variables are continuous, there are no gaps between the bars however, in discrete case gaps should be left between the bars.