A view at rear and bottom.
The subrack is mounted in its stands so, that USB and other interface cables from the rear can pass through to the front, as shown here:
The supply voltage / charge current indicator and the power switch:
Voltage and current are shown alternately. Above, 5,18 V are displayed, below, 0,49 A.
Here is shown, how the USB switch is been operated. The momentary-contact toggle switch is surrounded by LEDs indicating which tablet has been selected.
The activity LEDs of the RS-232 interfaces: