This is a fine mutual conductance tube tester made by one of the best tube tester companies, Hickok. The tester is complete with a smoothly operating tube chart roll, obsolete tube chart, foreign tube chart and operating manual. The outside of the case shows minimal wear, which is unusual for tube testers as they were often beat around. This 6000A is in excellent working order and was calibrated and electrical contacts cleaned and lubricated on 2 25 2012. Ferrite rings are also on the wires from the sockets which controls possible oscillation, which can adversely affect correct readings. This tester will give you many years of use and will assure you of your tubes condition before use in your valuable equipment. Please look at my feedback to see that it is all positive.