To demonstrate the mechanics of writing and using Reality Check equations, it is useful to work through a very simple example. Suppose that you want to model the growth of yeast in a bowl of water. The water is held at a constant temperature that can be set, and has a fixed amount of sugar in it to start.
We first list some of the Reality Check equations that must be satisfied:
| • | If temperature is below 50 degrees yeast growth should stop, and the yeast go dormant. |
| • | If temperature is above 100 degrees the yeast should die out. |
| • | If there is no sugar and the yeast are not dormant the yeast should die out. |
| • | If there is no water and the yeast are not dormant the yeast should die out. |
| • | If the yeast continue to grow they will consume all the sugar. |
| • | If the yeast continue to grow they will consume all the water. |
The other thing we know is that yeast reproduce by dividing and that when conditions are right they can reproduce with a doubling time of about 10 minutes.
