When electric dryers appeared on the market more than forty years ago, the housewife guessed how many minutes it would take to dry the clothes. This was an inexact science, at best, and twenty years or more later, schemes were invented to sense when the clothes were dry and to shut the dryer off. Some of the designs to sense moisture in clothes were very complex. Various sensors were imbedded in the back wall of the dryer drum. Most of them were based on measuring the increasing resistance of something when the moisture content of the drum decreased. As often happens, the complexity of the moisture measurement systems led to reduced reliability and even ruined clothes!
