Four sets of data are presented. The first is measures of tire wear by two methods, the so-called weight method and the groove method. The second is Gosset's famous example of corn yield from split plots of regular and kiln dried seed. The third set is waiting times between eruptions of Old Faithful geyser for two different periods. The fourth set is Michelson's 1879 determinations of the speed of light and a smaller sample of measures made by him in 1882. The data present the student with two situations in which a test for difference between sample means is called for and two in which a test for mean paired difference is called for.