The Holter monitor is a tool that measures the blood pressure. Clinical and physical examination provide little information about hypertension. However, sometimes making a casual measurement is enough to know if the blood pressure is high. The monitoring of the blood pressure consists in performing at least three tests on three different occasions. The patient should be sitting comfortably and with the forearm resting, forming a right angle. The measuring device has an inflatable cuff with a pressure gauge that should be calibrated frequently. In the case of obese children and adults appropriate cuffs according to the thickness of their arm should be used to calculate the systolic pressure. To assess the results, you must consider several factors: the temperature of the room (must be nice), the clothing should not compress the arm, and above all, do not eat, smoke or be exposed to the cold at least 30 minutes before running the test.