Timing. I have a camsew machine. It has a coged belt and I took the belt off and now that I have

Question

I have a camsew machine. It has a coged belt and I took the belt off and now that I have the belt on I think I have it out of time. How do I time the top gear to lowe gear? It has a tag on it that says 125, I cant find any other #. I see an Arrow on the lower gear but I cant find any thing on the upper pulley? please help? thanks gmann