The amount of money you save (and invest) isn't accurately depicted with this though. Living expenses don't necessarily grow with take home, if you keep lifestyle creep to a minimum.
So what this means is that if you make $100k and save $10k/year, if you start making $200k you can save the same $10k/year, plus the entire additional $100k after taxes (let's just say that's $50k+). So you doubled your salary but your savings went up 6x+.
This is all based, most likely, on Griffiths' textbook. Quoting here from this post https://www.reddit.com/r/Physics/comments/1b97gt/magnetic_fields_do_no_work_but_magnetic_cranes/ :
tl;dr: use Jackson ;)