Calendar, published by the medical science publishing house Wilhelm Maudrich, Vienna/Düsseldorf. Written by Dr. Hermann Knaus. First edition, 1934. Our copy is from 1953, the year of the 18th – 22nd editions. This calendar was also printed in Danish, English, Italian, Norwegian, Swedish, French, Dutch and Spanish. Enclosed is a counting stick to determine the dates of the fertile days in the menstrual calendar after Prof. Dr. H. Knaus.