G'day D2gary, the current printed and bound format of the Performance Handbook dates back to Edition 1, Dec 1970, but earlier versions existed as bound versions, and were also referred to as Salesman's Handbooks, where the page inserts were updated by Cat over time. Hardcopy versions were ceased with Edition 45, and then Cat made an announcement even the electronic versions would cease with Edition 49. This was due to resources from the Product Groups not being available or willing to provide the data to update the books, and because specifications and models change so quickly now, it was felt other online sources of such information would be more cost effective. Then out of the blue an Edition 50 appeared online for dealers - unfortunately it is a much scaled down version, contains more earthmoving theory and fundamentals and is no longer the 'salesman's bible' for current specifications. if you go to the FORMER MODELS section on you book you will see some historical information. Cheers Glen