Thanx for that - its really interesting - wish I had found this forum sooner.
My hova bator is model1632 and so is a later model than the author talks about, it has 5 air holes constantly open so I don't think I need to remove the extra plugs until after the hatch (this is what the manufacturer recommends). The author seems to be setting humidity to the room rather than the incubator (which in turn gets through to the eggs through the air holes anyway). It seems to make sense. Wish I had known before.
All I can do now is wait and see what happens - fingers crossed!
And thanx again everyone for all your support.