As in earlier periods, the focus of the examination was classical Confucian texts, while the bulk of test material centered on the Four Books outlined by Zhu Xi in the 12th century. Ming era examinations were perhaps more difficult to pass since the 1487 requirement of completing the "eight-legged essay", a departure from basing essays off progressing literary trends. The exams increased in difficulty as the student progressed from the local level, and appropriate titles were accordingly awarded successful applicants. Officials were classified in nine hierarchic grades, each grade divided into two degrees, with ranging salaries (nominally paid in piculs of rice) according to their rank. While provincial graduates who were appointed to office were immediately assigned to low-ranking posts like the county graduates, those who passed the palace examination were awarded a "jinshi" ('presented scholar') degree and assured a high-level position. In 276 years of Ming rule and ninety palace examinations, the number of doctoral degrees granted by passing the palace examinations was 24,874. Ebrey states that "there were only two to four thousand of these "jinshi" at any given time, on the order of one out of 10,000 adult males." This was in comparison to the 100,000 "shengyuan" ('government students'), the lowest tier of graduates, by the 16th century.