The video above shows a great demonstration on how the (HUD) Heads-up Display works for the Cadillac ATS and XTS. Learn how to move the HUD display, change which display to show (radio, speed, etc.), speed RPM warning and change the brightness of the display.
Over on Amazon they have a HUD Head Up Display 5.5″ for all Cadillac model 2003+ for around $99.95 plus shipping and handling.
Here are a few other tutorials on HUD heads up display settings: