The tensioned screens are characterized by a system of rubber bands or strings, which causes the screen is stressed avoiding wrinkles or malformations of the screen and the image can be as sharp as possible. It is considered that under normal conditions of humidity and temperature, a "normal" screen does not catch waves. All and so it is advisable to select a tensioned screen if its use is continuous since pantaTthe "normal" eventually caught slight undulations.

The 4: 3 format has long been used in the standard PAL TV and PC screens.
For every 4 horizontal elements 3 elements are present in your vertical. That is, it is a square image format where the horizontal distance substantially equal to the vertical distance.