Replying to myself... I wonder what book that was. It was a large slim hardback published sometime in the 1970s, around A4, so much earlier than the 1987 book.

Replying to myself... I wonder what book that was. It was a large slim hardback published sometime in the 1970s, around A4, so much earlier than the 1987 book. I don't have any course materials any more. As I recall, they argued that making a change in the requirements specification was ~10 times cheaper than finding and fixing a bug while writing the implementation, which in turn was ~10 times cheaper than fixing it after delivery, ie. on other people's production computers at other site. There was some argument around it, but the text didn't imply exactness, as far as I can remember.