Sahl lived in the first half of the 9th century. His five short treatises, Introduction to Astrology, The 50 Precepts, Judgments of Questions, Elections, and The Book of Times, appear to be the principal medieval source of rules for Horary Astrology and Elections. They constitute a corpus of detailed instruction for these two branches of Astrology.James Herschel Holden, the translator, is Research Director of the American Federation of Astrologers and is especially interested in early astrological works.