Chief judges have administrative responsibilities with respect to their circuits, and preside over any panel on which they serve unless the circuit justice (i.e., the Supreme Court justice responsible for the circuit) is also on the panel. Unlike the Supreme Court, where one justice is specifically nominated to be chief, the office of chief judge rotates among the circuit judges. To be chief, a judge must have been in active service on the court for at least one year, be under the age of 65, and have not previously served as chief judge. A vacancy is filled by the judge highest in seniority among the group of qualified judges. The chief judge serves for a term of seven years or until age 70, whichever occurs first. The age restrictions are waived if no members of the court would otherwise be qualified for the position.
When the office was created in 1948, the chief judge was the longest-serving judge who had not elected to retire on what has since 1958 been known as senior status or declined to serve as chief judge. After August 6, 1959, judges could not become or remain chief after turning 70 years old. The current rules have been in operation since October 1, 1982.
The court has eleven seats for active judges, numbered in the order in which they were initially filled. Judges who assume senior status enter a kind of retirement in which they remain on the bench, while vacating their seats, thus allowing the U.S. President to appoint new judges to fill their seats.
^Mack did not have a permanent seat on this court. Instead, he was appointed to the ill-fated United States Commerce Court in 1910 by William Howard Taft. Aside from their duties on the Commerce Court, the judges of the Commerce Court also acted as at-large appellate judges, able to be assigned by the Chief Justice of the United States to whichever circuit most needed help. Mack was assigned to the Seventh Circuit upon his commission.