def initialize(self, originalTimeSeries, calculatedTimeSeries):
        """Initializes the ErrorMeasure.

        During initialization, all :py:meth:`BaseErrorMeasure.local_errors` are calculated.

        :param TimeSeries originalTimeSeries:    TimeSeries containing the original data.
        :param TimeSeries calculatedTimeSeries:    TimeSeries containing calculated data.
            Calculated data is smoothed or forecasted data.

        :return:    Return :py:const:`True` if the error could be calculated, :py:const:`False`
            otherwise based on the minimalErrorCalculationPercentage.
        :rtype: boolean

        :raise:    Raises a :py:exc:`StandardError` if the error measure is initialized multiple times.
        """
        # ErrorMeasure was already initialized.
        if 0 < len(self._errorValues):
            raise StandardError("An ErrorMeasure can only be initialized once.")

        # sort the TimeSeries to reduce the required comparison operations
        originalTimeSeries.sort_timeseries()
        calculatedTimeSeries.sort_timeseries()

        # Performance optimization
        append      = self._errorValues.append
        appendDate  = self._errorDates.append
        local_error = self.local_error

        minCalcIdx  = 0

        # calculate all valid local errors
        for orgPair in originalTimeSeries:
            for calcIdx in xrange(minCalcIdx, len(calculatedTimeSeries)):
                calcPair = calculatedTimeSeries[calcIdx]

                # Skip values that can not be compared
                if calcPair[0] != orgPair[0]:
                    continue

                append(local_error(orgPair[1:], calcPair[1:]))
                appendDate(orgPair[0])

        # return False, if the error cannot be calculated
        calculatedErrors    = len(filter(lambda item: item is not None, self._errorValues))
        minCalculatedErrors = self._minimalErrorCalculationPercentage * len(originalTimeSeries)

        if  calculatedErrors < minCalculatedErrors:
            self._errorValues = []
            self._errorDates = []
            return False

        return True