Linn's U.S. Plate Number Coil Handbook by Ken Lawrence (1989, Hardcover)

If you can find this book it is a must for PNC collectors (Plate Number Coil Strips). It goes through how PNCs got started in 1981 after the total screw-up of the Post Office over plate blocks. The 18 cent flag started this 27 year long run of collectors who now view coil stamps in a different world. Ken's book covers technical data better than anyone could at the time (maybe because of his position with Linn's). But what makes this book a real gem are the photos of the stamps and strips Ken was able to buy/collect/borrow. It includes some very attractive imperfs and other fascinating printing errors.
The book is a little dated now that several others have covered more years, but for the first 9 years this book is a homerun. The only thing that wasn't included was guesses at approximate values of each strip.
If you are able to find this book on eBay- snap it up, you won't regret it.