Official Price Guide to Glassware

I have found this guide to be quite useful in establishing the value of some pieces of glassware. It is organized fairly well and is especially suited to collectors of depression and carnival glass. It would be more useful to me if there were more sections devoted to particular types of art glass,opalescent glass, vaseline glass, etc. However, given the enormity of the subject and the already formidable size of the book that may be impractical. As it is it is very valuable.