Learning to measure voltage is one of the basic skills of maintenance. It is a dangerous behavior to measure on the road. If necessary, we still need to do this. This behavior is not only our own safety problems, but also due to accidental damage due to operation. The possibility of the device is very large. If the measurement of the charger is broken, we should not be depressed or sad. The best mechanics will have errors, even if the master can't avoid it. As long as we remember that the measurement voltage has a clear purpose, do not blindly charge around, this is a big taboo.