The Hertz are a unit of frequency for measuring electromagnetic waves and vibrations. They are named after physicist Heinrich Rudolf Hertz
A hertz represents one cycle per second, meaning cycle as the number of vibrations that occur as the wave moves from an initial point until it returns to the same point.
The existence of two different types of frecuency is based in historical reasons and not for thecnical reasons.
In united states the engeniers from Westinghouse decided to use a 60 hz frecuency and, at the same period the engeniers from Allgemeine Elektrizitats Gesellschaft (Berlin) decided to used a 50 hz frecuency.
There were more frecuencies at that time, but 50 and 60 Hz become the most used.
The other countries decided what frecuency used in bases of their relasionships with eeuu and Germany.
Both frecuencies are quite similar and even with their diferences there is not one better that the other.
What frecuency I need
Now these days the 50 hz is the most common frecuency.
We also can find coutries with 60 hz it is very common in America
At any case we recommend you to Consult the next map