New Benz diesel owner and I cannot understand the Benz oil terminology, specs, grades!

Book says you can pick from about 17 specs (the 722.xx) and each one of those has heaps of different grades. Argh. Not used to this, I am used a spec (the letter cleanliness one) and a temp graph to pick what viscosity.

W164 and w211 both with om642.

Thanks