The (much) more advanced version of the Sega Model 1 I/O board is now emulated. One of it's features is that you can attach an LCD module (likely part of some test harness) and run it in a diagnostic mode. Some screenshots:
You can choose between nine different tests using the buttons on the I/O board itself.
Netmerc is in 'parameter display' mode by default:
You can also attach a serial terminal to it and run it in some kind of debug console mode where it supports various commands. See the source for details.
The display of the LCD screen is disabled by default, if you want to see it you need to switch to the 'Diagnostic' view in the video options.