'Sets the sign of the variation of this heading.
@param sign: The new sign. C{1} for positive and C{-1} for negative
signs, respectively.
@type sign: C{int}
@raise ValueError: If the C{sign} parameter is not C{-1} or C{1}.'

def setSign(self, sign):

    if (self.variation.inDecimalDegrees is None):
        raise ValueError("can't    set    the    sign    of    an    unknown    variation")
    self.variation.setSign(sign)
