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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def start_delta_string(self):
 """A convenient string representation of how long after the run started we started. :API: public """

    delta = int(self.start_time) - int(self.root().start_time)
    return '{:02}:{:02}'.format(int(delta / 60), delta % 60)