'Given the proposed upper and lower extent, adjust the range
if it is too close to being singular (i.e. a range of ~0).'

def nonsingular(self, vmin, vmax):

    unit = self._get_unit()
    interval = self._get_interval()
    if (abs((vmax - vmin)) < 1e-06):
        vmin -= ((2 * unit) * interval)
        vmax += ((2 * unit) * interval)
    return (vmin, vmax)
