Edgar Dale's Cone of Experience is a visual model that classifies instructional messages based on their level of concreteness, from most concrete like direct experiences down to most abstract like verbal symbols. It is not meant to be a strict ranking but rather a guide to show how concepts are developed through more or less engaging experiences. The cone includes 11 categories of instructional materials like exhibits, demonstrations, and pictures. While useful, it does not provide exact rankings and should not be taken as a perfect representation of the learning process.