1994 V6 Harmonic Balancer

K i got my new harmonic balancer in today and i pretty much know exactly how to get the old one out and how to install the new one...the only thing i'm not sure of is when i put it in what do the markings and measurements on top of it mean...what do they have to be lined up with. it has a groove in the middle so i assume it can only go in one way. should i just mark the old one before i take it out? any ideas are greatly appreciated i'll be doing it tomorrow morning thanks.