Kristensson (1987: 212) considers /o/ before nasals to be the defining feature of the dialect of the West Midlands, stating that "it was the most conspicuous feature of the West Midlands (and still is), and it seems warranted to take the /o/ isophone
as the boundary for the West Midland dialect area".
Yep, called the Isophone
, the helmet contraption floats in a pool and, once you've popped your bonce inside, all other senses dwindle to a minimum.
One should bear in mind, however, that the Estonian dialect division, which was established in its modern form by Andrus Saareste (1932), takes into account mostly the spread of phonetic and grammatical phenomena or isophones