<P> Normally, a newly filed federal action is assigned by the clerk of the district court to a district judge and a magistrate judge (whose initials are then appended to the case number in most districts). In some districts, magistrates judges are assigned to work with certain district judges, although they may not do so on all categories of cases . In other districts, magistrate judges are randomly assigned to cases . The clerk runs a random selection procedure (in some courts, spinning a wheel) based on a list of all available district judges and then runs the same procedure based on a list of all available magistrate judges . </P> <P> In a few districts, starting with the District of Oregon in 1984, magistrate judges participate together with district judges on a unified list of judges available for new cases . A newly filed case can then be assigned to a magistrate judge for all purposes, subject to the ability of any party in the action to affirmatively decline consent to that procedure within a certain time period . Filing of such a declination causes the magistrate judge to return the case to the court clerk for a standard assignment to a district - magistrate pair . </P> <P> Because Article III of the United States Constitution vests the judicial powers in courts to which the judges are appointed for life (and which are therefore called Article III tribunals), decisions of a magistrate judge are subject to review and either approval, modification or reversal by a district judge of that court--except in civil cases where the parties consent in advance to allow the magistrate judge to exercise the jurisdiction of the district judge, and in which case appeals from the decision of the magistrate judge are heard by the United States Court of Appeals . The magistrate judges therefore operate under the authority of Congress to appoint "inferior courts", set forth in Article I, making them Article I judges . </P> <P> The Supreme Court most thoroughly delineated the permissible scope of Article I tribunals in Northern Pipeline Construction Co. v. Marathon Pipe Line Co., striking down the statute that created the original U.S. bankruptcy court . The Court noted in that opinion that the framers of the Constitution had developed a scheme of separation of powers which clearly required that the judicial branch be kept independent of the other two branches via the mechanism of lifetime appointments . However, the Court also found that Congress has the power under Article I to create adjunct tribunals, so long as the "essential attributes of judicial power" stay in Article III courts . This power derives from two sources . First, when Congress creates rights, it can require those asserting such rights to go through an Article I tribunal . Second, Congress can create non-Article III tribunals to help Article III courts deal with their workload, but only if the Article I tribunals are under the control of the Article III courts . The magistrate judges fall within this category of "adjunct" tribunals . All actions heard in an Article I tribunal are subject to de novo review in the supervising Article III court, which retains the exclusive power to make and enforce final judgments . </P>

What are three duties performed by a united states magistrate