Thornton 1793, p.35. (en) William Thornton, Cadmus or, a treatise on the elements of written language, illustrating, by a philosophical division of speech, the power of each character, thereby mutually fixing the orthography and orthoepy, Philadelphia, R. Aitken & Son, (lire en ligne)
Schmeller 1827. (de + bar) Johann Andreas Schmeller, Bayerisches Wörterbuch, Stuttgart & Tübingen, Cotta, (lire en ligne)
Avram 1973. Andrei Avram, «Sur le statut phonologique de la voyelle neutre en catalan», Revue roumaine de linguistique, vol.18, no5, , p.399-405 (lire en ligne)
Eesti Keele Instituut / Institute of the Estonian Language
KNAB: Kohanimeandmebaas / Place Names Database, Taadi / Tat / Жугьури Džuhuri
latinisatsioon / romanization: KNAB 2012-09-30 - Notes-2: "In the earlier Azerbaijani Cyrillic there were variations: ə (= э)."