The operation manual of the original IBM PC from 1981 is a very good example.
Personal plug: I wrote an article about writing specs a while back. I use the IBM PC spec as an example, so you might find my article useful.
Personal plug: I wrote an article about writing specs a while back. I use the IBM PC spec as an example, so you might find my article useful.
Those three points are pure gold!
I'd also add that you don't need to be working on a major project to benefit from standing back to writing it out first. Much of what I write is just a few pages, but it's still useful. It saves time overall, helps others get up-to-speed fast, and is fun!