Fans of the book, what is your profession?

I'm curious to know what the people who are interested in a book like PHM do for a living/study. I imagine that that the population skews heavily towards engineering and science, but I'd like to know.

I read and enjoyed the book, but I am an aerospace engineer and the book was recommended to me by another aerospace engineer. Some passages in the book, like when he explains what a Fourier transform is, made me wonder if there are people who choose to read this sort of book and don't already know what a FT is.