HP Deskjet 812C demo page

To print a demo page from the Deskjet 812C (just to check printing ability or print quality) hold down the Resume button (the button below the Power button, with the arrow on it) for about five seconds.  A sample page with the printers model name and a color picture will print out shortly.

If youd rather print out a self-test page, which is all text but gives the printers serial number and page count, see the instructions here.