One’s sleep diary provides good information about their sleep timing, quality, and quantity, and is the best way to measure sleep if a person has insomnia. For more in-depth examination of sleep by scientists, or sleep medicine clinicians, special equipment is used to track sleep stages and cycles through the night. To determine sleep stages, three main measurements are used: brain waves, eye movements, and muscle tone. These are measured using electrodes that are attached to the scalp, the face near the eyes, and under the chin, respectively. Polysomnography is measurement of sleep overnight in the sleep lab, with electrodes that are attached to the scalp, face, and chin, to determine sleep stages. Actigraphy is another way that sleep can be measured, but only roughly.