I've read that the hydrometer isn't much use unless you use it at the
beginning and at the end of making the wine but I thought I'd test it
out on some wine I already started and I'm not sure what the readings
mean can anyone explain them to me please?

I've just bottled some gooseberry wine which I made from a tin of
concentrate (a kit) and it had a SG of 9 (I think thats 1.009?) I'm now
worried from what I've read that such a SG it might blow the corks out,
is that so? It had certainly finished bubbling and was clear when I put
the sugar in to make it taste nice several weeks ago.

I've got some elderflower wine which was started 2 months ago which is
really clear and not bubbling and it has a SG of .990. Can anyone tell
me what that means and what I should do about it?

Many thanks
flowerpot