There are two words in daily use that are related to the concept of uncertainty, accuracy and precision. In daily use, they are almost interchangeable, but in science they mean different things. The distinction between the two words is related to, but not the same as, the distinction between systematic error and random error, two important concepts to be looked at more closely in another session. To the left are four dartboards, used by four different players. It is easy to see that the four players differ in ability, but the patterns of dots where the darts hit also nicely exhibit the difference between precision and accuracy.