Of course you can think that you can not expect miracles of accuracy for a price of about 2.40. That's why I ordered 7 pieces although I really only needed 4. The plan was that by comparing measurements with my multimeters Device to select and give the inaccurate or dispose if necessary. After I had 4 pieces found in which the deviation is not greater than + - 0.1 volts was to my multimeters initially seemed everything as planned to run and I was - still - happy. (The deviation of the other three devices was between 0.2 and 0.4 volts) I then the 4 "good" ads on the cars distributed each placed in the glove box to test so then every 2 weeks times making the battery so. With the car in the garage which has a relatively old battery so I asked one of these famous testers determined that the voltage dropped below 11.5 volts and have downloaded the battery then. Unfortunately reloading brought after the usual loading time only meager 11.6 volts and the conviction that this battery should be replaced. After replacing the battery, the devil part then showed 11.8 volts - 1.1 volts enough !!!!
This means the display has not voted two weeks ago shows suddenly a Volt too little.
Conclusion .: The thing is cunning !!!
Supplement .: Yesterday I the voltage at said carriage again with two of these testers "measured". One showed 12.6 volts, the other 11.4 volts. This is exactly the difference between - good state of charge and must be recharged. Such deviations I can no longer recognize where here the benefits of this bone should be.
Second supplement .: After a few weeks the second tester is then totally failed and has shown nothing. The part can be disassembled but so I could make a backup behind the cold solder joint and resolder. Now both devices show back to the same value. So people who like to tinker and may simply have too much time in your life are helped with this product!