My first 8x10 film was seriously out-of-date Kodak Plus-X that a mate gave away because he wouldn't trust it for commercial work. I set up the camera looking at a front-lit "standard scene", grass, trees, houses, sky , clouds, etc and did a series of stepped exposures on a single 8x10 sheet. This is easily done by moving the film-holder dark-slide 50mm (say) between clicks and keeping track of f-stops and shutter speeds. I got an EI = 50 result with obvious base fog. Since I was going to use the negatives for contact work I set EI = 25 on my light meter. Big film loves extra exposure especially if it has lost sensitivity through age.