I'm working on a story and need a measurement system for them. So far, I have a tick for small measurements (think centimeter or inch), a mark for a bit larger (like a decimeter or foot) a 5-mark for large items ( instead of a meter or yard) but I need a name for the replacement for long distances like a kilometer or mile.

Does anyone have any suggestions?

Well, since you have a tick, maybe a klick for large distance.

tick, mark, 5-mark, span, 5-span, 10-span, reach, stretch.

And to teach the youngin's:

(the kids walking in place singing) 1-tick, 2-tick, 3-tick, Four, take a step and mark some more, (the kids start marching in place faster) 2-mark, 3-mark, 4-mark, Five, pick up the pace and run a span, (now the kids are running in place) 2-span, 3-span, 4-span, five, go any more and you need a horse, (the kids start galloping in place) 2-reach, 3-reach, 4-reach, Five, another step and you need a boat, (the kids pretend to be swimming) 1-stretch, 2-stretch, 3-stetch, Four... any more and you'll fall off the edge (and this is where all the kids fall down dramatically).

Thanks. I like that.