Big Goober: Can ya measure line weight?

Well, I think I gobbed out and have mislabeled a spool. I have a Tioga reel w/ two spools. One spool has SA GPX WF-5-F. The other spool has SA GPX WF-6-F. How can I tell the difference? I have a micrometer used for reloading, will that help?

Gobble butt!