Who used to present the swingometer on election night

[Dowser]

Giogle says it’s peter snow
But I seem to remember an old chap, long arms swinging like windmills and longish grey hair flapping about

Was fascinating watching him .., even though the subject matter was quite boring

Peter Snow.

Peter Snow.He really loved his swingometer

He took it over from a Canadian guy whose name I cannot remember.

It might be Robert McKenzie if you go further back....

en.m.wikipedia.org/wiki/Robert_McKenzie_(psephologist)

I was going to say Robert McKenzie.

Professor Bob Mckenzie

When Professor McKenzie died, Private Eye had a cartoon of a group of people having a seance to ask 'what's the swing, Bob?'.