Many other financial books recommend developing income streams outside of selling your labor at an hourly or yearly rate, which would seem to be missing from your book.
I am salaried, but when I sat down and calculated my hourly rate, I was a little shocked. I didn't factor in benefits or anything besides my after tax take home pay. It's as simple as $(2 week paycheck) / 80. What you get is effectively your hourly rate.
As a salaryman, knowing this value will help you avoid working overtime since overtime is unpaid. The more hours you work, the less your effective hourly rate. I would argue that if you are asked (either implicitly or explicitly) to work more than 40 hours a week, you should find a different job as you are diluting your own pay.