 He also developed a system, based on the phases of the Moon, that would allow a doctor to determine in advance the most critical days of a patient's illness.During the Arabic-Latin translation movement of the 12th century, "De Gradibus" was translated into Latin by Gerard of Cremona.Al-Kindi's mathematical reasoning was complex and hard to follow; Roger Bacon commented that his method of computing the strength of a drug was extremely difficult to use.