According to Wiedenhof's A Grammar of Mandarin, page 44,
"Weng" syllables rhyme with the fnal -ong [ʊŋ]
However, he'd specified weng as [wʌŋ], to add
Weng displays the same type of variation as the fnal -un: it may lose its rounding toward the end, [wəŋ].
Page 66 reads
there's free variation between [wʌŋ] and [ʊŋ] for both fnals, with complementary distribution
Can somebody please clarify the apparent ambiguities?
In the second paragraph, what does end refer to?