'_YBounds(Graph,float,float)
graph           parent object to calculate scales for
minimum_scale   minimum range to show on the graph
buffer          amount of padding to add above & below the
displayed temperatures. Given as a fraction of the
total range. (Eg .05 to use 90% of the range for
temperatures)'

def __init__(self, graph, minimum_scale=5.0, buffer=0.1):

    self.graph = graph
    self.min_scale = minimum_scale
    self.buffer = buffer
    self.update_freq = 10
    self._last_update = self.update_freq
