Chain Tension

Hi

I am the proud owner of an XJR 1300 and the maintenance is a bit of mystery
to me but i am learning. Can anyone advise me how far up the swinging arm i
should test the chain tension / slack??

Now the book says it should be 2 to 3 cm slack. I've just had a push the
chain and it was hitting the rubber chain cover on the under side of the
swinging arm at the top end. I made this too slack so have adjusted it and
it now moves about 2 cm in this position.

Any advise for a girlie trying to get it right would be much appreciated

Liza