The required n attribute is the number of characteristic measurements in this set.
Source
<xs:complexType name="CharacteristicMeasurementsType"><xs:annotation><xs:documentation>The CharacteristicMeasurementsType defines a list of characteristic measurements.</xs:documentation></xs:annotation><xs:sequence><xs:element ref="CharacteristicMeasurement" maxOccurs="unbounded"><xs:annotation><xs:documentation>Each CharacteristicMeasurement element gives information about a characteristic measurement.</xs:documentation></xs:annotation></xs:element></xs:sequence><xs:attribute name="n" type="NaturalType" use="required"><xs:annotation><xs:documentation>The required n attribute is the number of characteristic measurements in this set.</xs:documentation></xs:annotation></xs:attribute></xs:complexType>
<xs:attribute name="n" type="NaturalType" use="required"><xs:annotation><xs:documentation>The required n attribute is the number of characteristic measurements in this set.</xs:documentation></xs:annotation></xs:attribute>