This was the digital zone system book I've been looking for since digital was a thing. It assumes that you already have a working knowledge of the Zone System as Ansel Adams understood it (i.e., you've read Adams' work), and then builds from there.
When I shot film, we used a densitometer and a roll of bracketed exposures of a gray card to determine the trustworthiness of our camera's light meter. I have never been able to find a modern take on that, until reading Varis' book. He gives step-by-step instructions for determining your camera's dynamic range (not all sensors are created equal, even in cameras of the same model) and color fidelity, and then he provides the lightroom/photoshop techniques to bring out the most in your photos (n+/n- development times, for the seasoned photographers among us).
Check this book out from your library (the list price is $40), do the exercises therein, and take good notes.