"Such an instrument is composed of a linen or silk cord, to which, as you can see, a lead weight is attached which, after being struck, if the string is long, the movement of the weight will be slower and less frequent, if the string is short, its movement will be faster and more frequent. Therefore, when we want to measure the pulse rate, we guide the weight with our fingers, lengthening or shortening the string until we reach the point where the movement of the weight exactly coincides with the movement of the arterial wrist " from Santorio S., Commentaria in primam Fen first books Canonis Avicennae , 1625.