You can't make what you can't measure because you don't know when you've got it made.
--Dr. Irving Gardner
We've traveled far, and learned much along the way. We waded through all these details in search of an eat watch: a way to know, day in and day out, how much to eat to achieve any weight goal we choose. And now we know exactly what an eat watch must do, if not yet how to make one.
In chapter we learned how the human body gains and loses weight: by eating too many or too few calories compared to what it burns. Further, we discovered that for most of us, adjusting the amount we eat--what goes into the rubber bag--is the only practical way to control our weight. Therefore, an eat watch must be able to measure the balance of what goes in and what gets burned: to calculate whether we're getting enough, too little, or too much food.
In chapter we learned why some people constantly gain weight, while others maintain a constant weight, and still others seem trapped on a rollercoaster of gain and loss. It became clear that the mechanism, if not the cause, of most weight problems is a lack of negative feedback: a failure to adjust, by appetite, the amount eaten to the amount burned. The eat watch must then provide feedback, in a manner that will stabilise the system: allow you to achieve and maintain your desired weight.
The eat watch began as a mythical device, a miracle cure beyond reach. But along the way we've collected enough information about the body and about feedback to design something that does the job.