Let's begin with an explanation of the difference between accuracy and precision. Accuracy refers to how close a measurement is to the true value of what is being measured. Precision refers to how close measurements of the same quantity are to each other, even if they are not close to the true value. For example, the darts on the dart boards below represent sets of measurements. A bull's eye represents a perfect measurementa measurement exactly the same as the true value.
NEITHER PRECISE NOR ACCURATE Since none of the darts are close to the bull's eye, the
measurements they represent are not very accurate. Also,
since the darts are not very close to each other, the set of
five measurements here is not very precise either.
BOTH PRECISE AND ACCURATE 

The measurements are all close to the true value, so they are accurate. Also, the measurements are all close to each other, so they are precise. 
PRECISE BUT NOT ACCURATE 

Since all of the measurements are close together, they are precise, but since they are not close to the true value, they are not accurate. 
Since all of the measurements are close together, they are precise, but since they are not close to the true value, they are not accurate.
Activity 1:
See if you can draw and describe (as done in the pictures and captions above) the case where a set of measurements is fairly accurate but not very precise.
Activity 2:
For Dave students: Each student measures the diameter of the cylinders various cars and record the measurements in a spreadsheet as following:
Cylinder 1 2 3 4 5 6 7 8 1 ______ ______ ______ ______ ______ ______ ______ ______ 2 ______ ______ ______ ______ ______ ______ ______ ______ 3 ______ ______ ______ ______ ______ ______ ______ ______ 4 ______ ______ ______ ______ ______ ______ ______ ______ 5 ______ ______ ______ ______ ______ ______ ______ ______ 6 ______ ______ ______ ______ ______ ______ ______ ______ 7 ______ ______ ______ ______ ______ ______ ______ ______ 8 ______ ______ ______ ______ ______ ______ ______ ______
Diameter
FOR ALL STUDENTS:
For high school students in DuPage county: Draw a dart board on a sheet of paper and set it on the ground. Have each member in a group of about five drop a penny on the target from a height of about one meter, aiming for the bull's eye. Each penny represents a measurement of some quantity, say, the compression in the cylinder.
Now simulate a new set of measurements by dropping pennies from a height of 2 meters.
Activity 3:
For high school students in DuPage county: Suppose your team is challenged to determine the mass of an object using a balance. Each member of the team measures the mass on the same balance. Here are you data:
Team member 
Mass in Grams 

1 
39.97 
2 
40.06 
3 
39.98 
4 
39.97 
5 
40.02 
Your team decides to report your mean (average) mass, which is 40.00g. Your instructor then informs you, however, that the actual mass is 45.00g.