'Updates graph.minyvalue and graph.maxyvalue based on current
temperatures'

def update(self, forceUpdate=False):

    self._last_update += 1
    if (forceUpdate or (self._last_update >= self.update_freq)):
        (self.graph.minyvalue, self.graph.maxyvalue) = self.getBounds()
        self._last_update = 0
    else:
        bounds = self.getBoundsQuick()
        (self.graph.minyvalue, self.graph.maxyvalue) = bounds
