On the countertop, we have a collection of several different kinds of objects. We want to make lists, and put the objects into order according to our observations of the objects.

For example, we can count the sides (or facets or planes) of the objects, and list them in order from one side through the highest number of sides. How many sides does the pencil have? How many sides does the needle have? How many facets does the crystal have?

Let's list them again, in order, according to their size. We could even do that twice, because we could use their measurements in inches, and then we could weigh them.

Now we'll make another list, in order according to their colors, from light to dark.

Why do we do this?