'Advance the current progress, and redraw the screen.
:param incr: Raise the current progress by this amount. Default: 1'

def tick(self, incr=1):

    self.current += incr
    if (self.current and ((self.current % self.milestone_stride) == 0)):
        now = datetime.now()
        duration = (now - self.milestone_time)
        duration = (duration.seconds + (duration.microseconds / 1000000.0))
        rate = (self.milestone_stride / duration)
        remaining = (self.total - self.current)
        self.estimated = int(((remaining / rate) / 60))
        self.milestone_time = now
    self.draw()
