The maximum tenure in office was nine years, but every three years officials were graded on their performance by senior officials. If they were graded as superior then they were promoted, if graded adequate then they retained their ranks, and if graded inadequate they were demoted one rank. In extreme cases, officials would be dismissed or punished. Only capital officials of grade 4 and above were exempt from the scrutiny of recorded evaluation, although they were expected to confess any of their faults. There were over 4,000 school instructors in county and prefectural schools who were subject to evaluations every nine years. The Chief Instructor on the prefectural level was classified as equal to a second-grade county graduate. The Supervisorate of Imperial Instruction oversaw the education of the heir apparent to the throne; this office was headed by a Grand Supervisor of Instruction, who was ranked as first class of grade three.