Large Flat Panel Monitors Are Flat Panel Monitors Measured The Same As CRT's?

Are flat panel monitors measured the same as CRT's? - large flat panel monitors

I've heard that are not the CRT and flat panel displays, the same meaured. Considering that CRTs are measured diagonally, flat panel displays measuring somehow a little different. Thus, according to my sources, a 18-inch flat screen is actually much larger than a 18 "CRT.

is that true? exactly what suited the display of flat screens? All links to the sources (eg, diagrams, etc.) would be greatly appreciated.