A buddy at the diner in Tulsa asked how I check if my oven is level, and his reason why stuck with me
He bakes a lot of layer cakes and said a 2 degree tilt is why his tops kept coming out lopsided on one side. I never once checked mine. Went home, put a bubble level on the rack, and sure enough the back left corner is low by a hair. Now I'm wondering how many of my sunken middles were never the recipe at all. Checked the level on a marble slab too and it was fine, so it's the oven feet. Has anyone shimmed their oven legs and actually gotten a flat cake out of it? I don't want to mess with it and make things worse.