Although there are various ways (which I'm not personally familiar with), hours of SNLT may be a starting point for more complex calculations. It doesn't apply for management positions (or really positions which don't produce a non-reproducible good), though I'd be interested to see where the research in that's going.
I'm not sure why my comment was downvoted, especially without explanation. I thought it's quite reasonable for a person to be paid as much as he or she works.