4.2 Frequency Diagram
A bar chart is used when the statistical material can only have certain values, for example numbers. Normally the numbers represent a number of something (observations).
A survey was done in a class about how many siblings each student had.
There were 23 students in the class.
The results were written up in a frequency table. The observations in this case are the number of siblings.The frequency indicates how many students have a certain number of siblings. For example, there were four students who had three siblings.
Frequency Table
Then a diagram is drawn. It is important here to remember to use a straight edge and be careful that every mark has the same distance between them. 

In a bar chart, there are two axis; the x and yaxis.
On the yaxis, the vertical one, the frequency is normally given. In other words, how often something occurs. On the xaxis, the horizontal one, observations are recorded.
