In plotting a histogram, one must decide whether to include a datum that lies at a class boundary with the class interval to the left or the right of the boundary. The rule for making this assignment is called an endpoint convention. The two standard endpoint conventions are (1) to include the left endpoint of all class intervals and exclude the right, except for the rightmost class interval, which includes both of its endpoints, and (2) to include the right endpoint of all class intervals and exclude the left, except for the leftmost interval, which includes both of its endpoints.