Astrologers in sixteenth-century Europe were tasked with making a variety of different types of predictions. They used the practice of annual revolutions to predict weather or other potential natural disasters for the upcoming year. The practice known as elections helped them to determine the most propitious days and times for undertaking journeys, going to war, getting married, or laying the foundation for a new building. And they engaged in the standard astrological practice of nativities, or casting horoscopes predicting the details of an individual’s life. According to the wisdom of the second-century CE astronomer-astrologer Claudius Ptolemy, knowing the future enabled one to adequately prepare one’s soul for the calamitous or the fortunate. Calculating the length of a client’s life was part of the standard procedure for nativities, although by the sixteenth century, the precise method for this procedure was far from straightforward. Much of the confusion surrounding this calculation was related to two technical terms which had been transliterated from Arabic-Latin translations of the twelfth and thirteenth centuries: the hyleg and alcocoden.