Harrington, Cox & Evans (1997) Harrington, J.; Cox, F.; Evans, Z. (1997), "An acoustic phonetic study of broad, general, and cultivated Australian English vowels", Australian Journal of Linguistics, 17 (2): 155–84, doi:10.1080/07268609708599550
Roach (2004:242) Roach, Peter (2004), "British English: Received Pronunciation", Journal of the International Phonetic Association, 34 (2): 239–245, doi:10.1017/S0025100304001768
Wikström (2013:45), "It seems to be the case that younger RP or near-RP speakers typically use a closer quality, possibly approaching Cardinal 6 considering that the quality appears to be roughly intermediate between that used by older speakers for the LOT vowel and that used for the THOUGHT vowel, while older speakers use a more open quality, between Cardinal Vowels 13 and 6." Wikström, Jussi (2013), "An acoustic study of the RP English LOT and THOUGHT vowels", Journal of the International Phonetic Association, 43 (1): 37–47, doi:10.1017/S0025100312000345, S2CID146863401
Verhoeven (2007:221) Verhoeven, Jo (2007), "The Belgian Limburg dialect of Hamont", Journal of the International Phonetic Association, 37 (2): 219–225, doi:10.1017/S0025100307002940
Peters (2006:118–119) Peters, Jörg (2006), "The dialect of Hasselt", Journal of the International Phonetic Association, 36 (1): 117–124, doi:10.1017/S0025100306002428
Darnal, Arnav. "Spoken and sung vowels produced by bilingual Nepali speakers: A brief comparison". Himalayan Linguistics. 23 (1): 5–11. doi:10.5070/H923161723.
Wikström (2013:45), "It seems to be the case that younger RP or near-RP speakers typically use a closer quality, possibly approaching Cardinal 6 considering that the quality appears to be roughly intermediate between that used by older speakers for the LOT vowel and that used for the THOUGHT vowel, while older speakers use a more open quality, between Cardinal Vowels 13 and 6." Wikström, Jussi (2013), "An acoustic study of the RP English LOT and THOUGHT vowels", Journal of the International Phonetic Association, 43 (1): 37–47, doi:10.1017/S0025100312000345, S2CID146863401