Traduzione in corso passo 2
Here's the backside! You can see the GPIB connector on the right. The rear terminals on the left. The strange open port upper left is where you can connect the 8 additional channels for reading voltages (or 4 channels of 4-wire resistance readings).
Remove the four screws and two "screw in threaded connectors" circled in red in the images.
The brown trim ring should come off easily.