Why are box and computer monitor screen measured diagonally?

Answer:

The deeply first monitor tubes were circular. That channel that the diagonal was equal to their diameter. Later on they more and more evolved to the square screen we have presently, and wide screen were added. No entrepreneur would deviate from mentioning the largest line on the eyeshade (its diagonal) as the screen's size as it would make their screen look smaller than those of the competition.
A diagonal is a good benchmark of surface. Remember Pythagoras?



diagonal squared = width squared * stage squared



So a 19 inch (diagonal) monitor is bigger than a 17 inch.



Most older monitors enjoy the 4 x 3 aspect ratio (width by height) which is similar to older TV's. The first computers in truth used a TV to display output.



Now TV's have gone widescreen, to 16 by 9 aspect ratio and computer monitors have followed. A widescreen computer monitor of 20 inches or more is suitable for showing two page side by side, in adjunct to showing your video in widescreen (if the video source is surrounded by widescreen format).