Buy a AMENDED PRINTED PATENT APPLICATION NUMBER 599,611 FOR IMPROVEMENTS IN OR RELATING TO... online at a discount. For additional info or to view another item in this category, click next item. To return to where you were, use the current page links below. Frequency Control and other engineering tools can be found in the Engineering Book Monster for a discount! 35 Frequency Control references are alphabetically sorted. Click on items for descriptions, reviews, price info, and more information. Also shop at Engineering Book Monster for textbooks on engineering theory and practice. Use our database search tool to locate specific titles, authors, and disciplines.