Which Canon Diopter?

[sniper x]

I have a few Canon A1's and AE1's and am getting another F1 system. I wear a +2.50 reader as general reading glasses and do not (at this point) wear regular prescription glasses. BUT even though I can adjust the diopter on my DSLR's to suit my eye, none of my old SLR bodies have diopters. SOOO, I need to know which diopter I need for the A1 and F1 (strength wise) so I can clearly see the viewfinder for focusing.