The best choice of display when looking for outliers is the boxplot. A glance at the boxplot of the Old Faithful dataset shows that this dataset contains no outliers. Note that the three displays complement each other in the information they provide about the data. One strong argument for the need to use computers and graphing calculators when studying statistics is the necessity of viewing the data in a variety of ways. Without technology to draw the graphs this would be impossible to do efficiently.
Clustering shows up most clearly on a dotplot.
The Old Faithful dataset shows two clusters centred around 2 minutes and 4.5 minutes. A dotplot shows granularity as stacks of dots separated by gaps. By default, discrete data has some granularity as only certain values are possible. Continuous data can show granularity if the data is rounded. The Old Faithful dataset shows evidence of granularity.