Auto-matic graphing.

Say you're running a car wash to raise money for a class trip. The Car Wash Hand-book says the more suds you have, the more customers you'll attract. Which soap gives you the most suds? To find out, you test four different kinds of detergent.

In a data table, you record your raw data. You now have a dizzying display of numbers that runs left to right, up and down.

How can you make sense of all those figures? Simply turn your data table into a picture--a graph.

Keep in mind: Graphs come in many forms. We'll show you how to make two: a bar graph and a line graph.

BAR GRAPHS

Bar graphs are the way to go when the variable you are changing (the independent variable) is discrete, meaning it comes in different types with no types in between. For example, lizards and spiders are different types of animals. There is no species halfway between a lizard and a spider--just other species.

In the car wash experiment, the detergent types, such as Tubmagic and Pink Laundry, are also discrete variables.

Note in the bar graph above that each detergent gets its own bar. Together, the bars help you draw conclusions about your results. Can you tell which detergent is sudsiest? How? How long would it have taken you to explain that by looking only at the numbers in your data table?

LINE GRAPHS

Line graphs tell a different story, a story that often describes changes over time. Say, for example, you're studying how long the suds of a given detergent will last. (The Car Wash Handbook says that if the suds last all day, so will your customers.) Now, instead of comparing bubble heights produced by different detergents, you want to compare how the bubble height for each detergent changes over time.

To find out, you measure the bubble height for each brand of detergent every five minutes for 20 minutes. In this case, your independent variable (time) is continuous. That means there are values (such as two minutes) in between the times you take measurements. Your data table might not list those in-between values. But with a line graph, you'll have an idea of what those values might be.

For example, on the line graph above, you can see that the height of Handsuds bubbles didn't drop suddenly from 5cm to 2cm. It changed gradually during the first five minutes of your experiment. What other trends can you spot?