Natural events outside the body served as indicators for selecting the time, site, and frequency of bloodletting during the Middle Ages when astrological influences dominated diagnostic and therapeutic thought. This is illustrated by the fact that the earliest printed document relating to medicine was the "Calendar for Bloodletting" issued in Mainz in 1457. This type of calendar, also used for purgation, was known as an _Aderlasskalender_, and was printed in other German cities such as Augsburg, Nuremberg, Strassburg, and Leipzig. During the fifteenth century these calendars and _Pestblatter_, or plague warnings, were the most popular medical literature. Sir William Osler and Karl Sudhoff studied hundreds of these calendars.[25] They consisted of a single sheet with some astronomical figures and a diagram of a man (_Aderlassmann_) depicting the influence of the stars and the signs of the zodiac on each part of the body, as well as the parts of the anatomy suitable for bleeding. These charts illustrated the veins and arteries that should be incised to let blood for specific ailments and usually included brief instructions in the margin. The annotated bloodletting figure was one of the earliest subjects of woodcuts. One early and well known _Aderlassmann_ was prepared by Johann Regiomontanus (Johannes Mueller) in 1473. It contained a dozen proper bleeding points, each suited for use under a sign of the zodiac. Other _Aderlassmanner_ illustrated specific veins to be bled. The woodcut produced by the sixteenth-century mathematician, Johannes Stoeffer, illustrated 53 points where the lancet might be inserted.[26] "Medicina astrologica" exerted a great influence on bloodletting. Determining the best time to bleed reached a high degree of perfection in the late fourteenth and fifteenth centuries with the use of volvella or calculating devices adopted from astronomy and navigation. These were carried on a belt worn around the waist for easy consultation. Used in conjunction with a table and a vein-man drawing, the volvella contained movable circular calculators for determining the accuracy, time, amount, and site to bleed for an illness. The dangers of bloodletting elicited both civic and national concern and control. Statutes were enacted that required every physician to consult these tables before opening a vein to minimize the chance of bleeding improperly and unnecessarily. Consultation of the volvella and vein-man was more important than an examination of the patient.[27] (Figure 3.)