That is the viewable screen real estate on that display.

Look down on right...

Technical Specifications

Screen size: 24 inches (diagonal viewable)
Screen type: TFT active-matrix LCD
Resolution: 1920 by 1200 pixels
Colors: 16.7 million
Viewing angle: 178° horizontal; 178° vertical
Brightness: 330 cd/m2
Contrast ratio: 1000:1

"If it turns out that President Barack Obama can make a deal with the most intransigent, hard-line, unreasonable, totalitarian mullahs in the world but not with Republicans? Maybe he’s not the problem."