Epson 20 - Manual (Page 161)

Once you examine this screen, press any key to display the next page.
The eight pages, numbered 0 to 7, are displayed sequentially.
After the eighth page appears, you see the prompt:
Is the display correct (Y/N)?
If all eight pages are correct, press Y and Enter. If any page is filled
with an incorrect number, press N and Enter to display the error
message.
Light Pen Check
To check the function of a light pen connected to the color graphics
adapter card, press 8 and then Enter. This test checks that a light
pen connected to the color graphics adapter is performing accurately.
When you select this check, you see these prompts:
Enter Y to start light pen check.
Enter N to return to the menu.
Performing System Diagnostics C-17