68 dart 318 troubleshooting challenge

I don't have a compession tester yet, so i took off a valve cover and turned the harmonic balancer by hand until I saw the #1 cylinder valves opening and the timing mark was not near the line on the block, I know this is not very conclusive, but the valves appear to be closed when the timing is set to fire off piston #1...

I'll buy a compression tester in the morning, I am too P.O.'d at my car to talk to the parts store people right now...

I guess I may as well ask this now.... How much compression is "really low"

ie: low enough to tell me my timing chain has slipped?

and, as always, thank you for letting me drink from the FABO fountain of knowledge!