. . . . . with the test chart (a cereal box with writting on it)
Ha! I did the same thing a couple of years ago when I tried to MFA a new lens. Problem was, I honestly can't tell when text is perfectly sharp, and when it is 'almost perfectly sharp'. I simply can't see the difference, despite having vision much better than 20/20.
I realized that there just isn't any fine detail on cereal boxes, and that fine detail is what I need to look at to determine sharpness.
Anything with hair or feathers should give you results that are much easier to interpret with accuracy. And when I say 'hair', I mean real hair - the artificial hair (fibers) on a blanket, or the trim around the hood on a winter coat, won't work. Use a mounted deer head or a mounted pheasant or something of that nature. Or if you have a dog that can stay perfectly still for long periods of time, that will work, too.