The VC-11R alternator tester is a handheld, very useful and easy to use device, used by car garages, diagnostic stations, authorised service stations and rebuilders.
The VC-11R allows you to diagnose an alternator that is communicating with the ECU of the car, when it’s still mounted. These "modern" alternators can't be diagnosed by using a regular voltage meter.
The ECU communication systems are found on cars starting from 2002 and up, and are known as LIN (Local Interconnect Network) and BSS(Bit Synchronous Single-wire) systems, and even earlier as Ford or GM's PWM(Pulse Width Modulation) systems.
The VC-11R is worlds only tester that allows you to read the commands demanded by the ECU and also send commands to the regulator.