Chain tension?

[Dogbad]

I'm not riding the XBR at the moment so it gives me less than 100% enthusiasm to work on it.
One simple question though is the Chain Tension.  How much play, up and down, should I have on the chain?
There seems a lot to me but I am a long time from doing mechanical stuff and I can't remember even a rough guide.

[pigafetta]

I go for about 1-1 1/2" slack with someone sitting on the bike. If you do it without weight it gets way too tight when you sit on it.

Dave B

[Dogbad]

Cheers Dave. Forgot about the weight on the seat etc!  Doesn't seem too far out at that but I'll double check it tomorrow (Today )