It means the cam and crank gears have multiple key-ways which allow the cam to be installed in either an advanced or retarded position. Installing the cam + or - will change the power band. Unless you have the knowledge to understand all the implications of this I would advise just installing it straight up, or dot to dot. I just can't see an advantage to this level of adjustability in a basically stock engine.
Wow at $289.88 that is one expensive timing set! I'm not saying it isn't a good set as I'm sure it is top quality, but I think it's awful expensive to use in something other than a purpose built race car.
Just for comparison I spent $40 for my steel geared, double roller timing set and ran 140 passes at the track this year with no problems.
It's your money you can spend it how you want, but if you have budget concerns like most of us the money you save can go towards other mods!
__________________ OFR - old fart racing
We're not the fastest car at the track but we might be having the most fun.
If you're not having fun, then you're taking this stuff too seriously! | 
Timming chain advance 
