We can define the paper formats according to their measures and these are defined in ISO standard 216 one, which in turn includes the standard DIN 476. This applies in most of the world. I there are plenty of measures for the role, but the most used are the Serie A and to a lesser extent Serie B.

In Serie A, the most widely used format is the A4 (210x297mm) or also called "sheet" used in most printers and fotocopiadoras.

Series B is defined for intermediate sizes Series A. For example, the B4 is the intermediate size between A3 and A4.

One hertz is one cycle per second, meaning repeating cycle as an event. For example, hertz is applied physics measuring the number of times for a second wave (either acoustic or electromagnetic) is repeated or can be applied, among other uses, to ocean waves that reach the Beach vibrations per second or a solid. The quantity that measures the frequency hertz is called,in this regard, the inverse of the period. One hertz is an oscillation frequency of suffering a particle over a period of one second.