Hypertension is a common cause of premature mortality yet has been amenable to pharmacologic treatment for more than 8 decades. Resting blood pressure fluctuates for various reasons, and individual responses to different classes of antihypertensive drugs vary considerably. In another high-risk common chronic condition, diabetes, glucose levels vary widely due to factors including individual drug response, physical activity, and carbohydrate intake. Patients treated with insulin are generally taught to adjust their insulin dose guided by self-measurement of glucose levels.