Master

In diagnostic and ECU tooling, master and slave describe how much a tool is allowed to do rather than how well it does it. A master version reads and writes freely and handles its own file encryption, while a slave is tied to a master for the files it can work with.

That difference matters most on resale and on shared work: a slave tool cannot stand alone. Check which version a listing covers before ordering, since the hardware is often identical and only the licence differs.