The cuff should be wrapped in such a way that it should not numb your hand. The pressure is to be created in hand later using the inflation pump, which records the blood pressure when it deflates. If the cuff is tight from before, then it will increase the blood pressure later. The cuff should also not be loose on the hand as it will loosen the grip of the stethoscope or the cuff if digital one. Either way, the device will not be able to provide the correct measurement. Thus, the cuff has to be tight enough so that two of the fingers can easily penetrate through it.