Isotope proportion is a number of atoms of each isotope in a sample of one element. It uses relative masses of isotopes to calculate a relative mass of one element.
Generalic, Eni. "Isotope proportion." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
Glossary
Periodic Table