Can someone help me read my chart please!

Karen

Hi, I’m hoping someone can help me figure out what all my different monitoring means. I am mostly confused with my opk and my cm. My question is, if I got a positive opk on cd24 but then had a fairly big dip in temp on cd28 and also happened to have the last day of fertile cm on cd28, which day did I possibly ovulate? Thanks for your help!