Each Decoder wheel provides a quick & easy references by just turning one of the 4 dials. The Aromatherapy Basic Decoder wheel provides quick & easy reference for uses & properties of 36 essential oils. Turn the disks and find the properties traditionally associated with each of the basic 36 Essential Oils. For more specifics on how much of each oil to use, you might wish to also try the Advanced Aromatherapy Decoder. Approximately 6" x 6" x 1/4".