During Galileo’s life, however, the properties of the pendulum were used to create one of the first medical devices invented: the pulsilogium. It consisted of a weight on a string, which was attached to a horizontal ruler. The ruler allowed the length of the string to be shortened or lengthened. By changing the length of the string, the pulsilogium allowed the doctor to adjust the period of the swing of the pendulum to match the heartbeat of the patient. Thus the length of the string provided a fairly reproducible measure of heart rate.7
