...the first number is for signal strength and the second number is for readability. Signal strength and readability are measured on a five point scale with 5 being the highest value possible and 1 being the lowest. So when you say to the controller (or pilot) “5 by 5”, it is literally another way of saying that the transmitter you hear is “loud and clear... 5/5 is also a damn good excuse to eat tocos and swill coronas,...eye yiyiyi!