I had to get this number here a while back, but unforetunately I don't remember what it was. But I do know I got it out of Human Factors design handbook. If you still need it I can run the book down and find it for you. But it would be best if you see it so you understand exactly how the the...
If you do a simple search on "Human Factors Handbook" you'll turn up more books with that kind of information than ever thought would exist. The one I've used is titled Human Factors Design Handbook. There is a Mil spec to it's number 1472.