Suppose that we are passing by a house and make the following observations:

• In the lawn the sprinklers are running.
• There are several measuring cups at various places in the lawn catching water.
• After 5 minutes of watching one of these cups, you notice that an additional 1 cup of water has accumulated.
• The cups have different amounts of water in them.
• There is a beautiful girl in a bikini sunbathing on the lawn.

Assumptions we might make:

1. The flow of the sprinklers is constant.
2. The coverage of the sprinklers is uniform.
3. The cups were empty when placed on the lawn.
4. The cups were placed on the lawn at different times.
5. No water was added to the cups other than by the sprinklers.
6. No water has evaporated from the cups.
7. None of the cups has a leak.
8. The girl did not drink from any of the cups.

Cup	Assumed Age of Cup in Sprinklers	Actual Time in Sprinklers
	This cup has 2.5 cups of water in it.  At the rate of one cup accumulated each 5 minutes, we "date" this cup as being in the sprinkler for 12.5 minutes.	Actually this cup started with 1 cup of water, so it is only 7.5 minutes old.
	This measuring cup contains 1 cup of water.  We "absolutely" date it as being on the lawn in the sprinklers for 5 minutes.	This cup has a leak and has actually been in the sprinklers for 15 minutes.
	This measuring cup holds 2 cups of water and we are positive it has been capturing water for 10 minutes.	The girl accidentally knocked this cup over after it was in the sprinklers for 2 minutes.  It has been on the lawn for 12 minutes.
	This cup is empty, so we believe it has just been placed in the sprinkler flow and has not caught any water yet.  It is "zero" minutes "old".	We are wrong again, the girl got thirsty and just drank it.
	And the final measuring cup we examine has half a cup of water accumulated.  Therefore, we can confidently say that it has been on the lawn for 2.5 minutes.	We are wrong again because the sprinklers were running at a higher rate before we made our observations.  This cup has only been in the sprinklers for 1 minute.

Back to Exhibit 13