Sets the numeric score increment.

        arg:    increment (decimal): the numeric score increment
        raise:  InvalidArgument - ``increment`` is invalid
        raise:  NoAccess - ``increment`` cannot be modified
        *compliance: mandatory -- This method must be implemented.*

def set_numeric_score_increment(self, increment):
        """Sets the numeric score increment.

        arg:    increment (decimal): the numeric score increment
        raise:  InvalidArgument - ``increment`` is invalid
        raise:  NoAccess - ``increment`` cannot be modified
        *compliance: mandatory -- This method must be implemented.*

        """
        # Implemented from template for osid.grading.GradeSystemForm.set_lowest_numeric_score
        if self.get_numeric_score_increment_metadata().is_read_only():
            raise errors.NoAccess()
        try:
            increment = float(increment)
        except ValueError:
            raise errors.InvalidArgument()
        if not self._is_valid_decimal(increment, self.get_numeric_score_increment_metadata()):
            raise errors.InvalidArgument()
        self._my_map['numericScoreIncrement'] = increment