Cake is defined as "a general term that refers to a vast array of baked goods ranging in texture from light and airy to rich and dense, and made in a variety of sizes and shapes. They may be single or multilayered, with almost endless flavour combinations"
Source: The Pastry Chef's Companion and my personal expertise as a pastry chef.
I use the appendix in The Pastry Chef's Companion. For anything else that's not back there, I measure it out, weigh it, then write it down in a notebook for future reference. Yeah, it's not the "true" ratio but it works well enough for me.
Also, good book. Try the Pan l'Acciene formula when you get a chance. It's unbelievable.