actually after rereading your issue i dont think its possible to have two differnt y axis scales but maybe if you create two charts then use paint to overlay one on the other.. but why would you want then on the same graph if its a differnt measurement?
i used to be an excell wiz back in school. i was a physics major and did sh*t like that all the time. i dont know if you can have two scales on the same axis. is it possible to set up a conversion factor such that all three are in the same units?