I'm suggesting nothing more complicated than printing out a few patches of gray that the spotmeter says are one zone apart. This for the purpose of creating a camera test. You could do same selecting patches of construction paper. Technically speaking, the values that correspond to the patches you create are part of a "transfer function" but I don't say take it that far. Just go far enough to create something you can shoot.
I have a two-tone target painted on plywood ... one zone apart to the spotmeter. This goes with Minor White's teaching.