Your new Jackson Model 658-1 Dynamic Output Tube Tester is the result of years of research, plus Jackson's wide experience in the manufacture of quality test equipment. It is. we believe, the finest service-type tube tester available. You will find your new tester accurate, fast, and easy to use. Because it offers so many more tests than are normally available on a tube tester, you may find it a little unfamiliar when you first start to use it. That is why we ask you to read this instruction book thoroughly before using your tester. Complete understanding leads to complete satisfaction. By thoroughly understanding the operation, you will be able to derive greater precision and profit from its use.