Dexter's discovery

You've seen the daily weight chart on page that so exasperated Dexter. You've seen, on page , the graph of Dexter's actual weight after correcting for all the variations caused by the momentary contents of the rubber bag. Consider this graph. The solid line is Dexter's true weight and the dashed line is produced by applying a simple mathematical procedure to the weight numbers from the scale, those foul figures that so vexed Dexter as he dieted.

Hidden all along among the random day-to-day variations in weight was what really mattered to Dexter: how much fat his body packed. All the despair, all the premature hope and subsequent betrayal could have been avoided had Dexter only known how to extract the truth about his body from the numbers on the scale.

We shall now learn how to do this.