Controllogix Tracking

I have an application where I am wanting to track rolls on a conveyor to center them for kick off. The rolls are different lengths and we will have a measuring eye to measure. Also, we have a prox switch counting teeth on the conveyor so we can track position. Now, I have done BSL's to track boxes before but I would like to calculate the distance of travel, then have the register index down to the kick off point. Would I use a FFL/FFU? I am not very familiar with these instructions but I was wandering if anyone had any suggestions. Basically, I can do the math of where I want the conveyor to stop based on the length from conveyor entry to the center of the kickoff. Also, I will take into account the roll measured length from the PE.

Thanks,

Maybe this will give you some ideas. Uses the COP Command for tracking.