It is quite simple, but perfectly OK for the price. It time to whether the individual wires pass.
If not, or at swap it shows on the LEDs.
If you have understood the principle, it is quite easy and so I have found that a port of my double socket was broken.
New clamped, measured by running. So be it, so it was worth the money.
As I said great for home use, price performance to be proud of.
