Each move is represented by a set of two, two-digit numbers: the start and the destination square, written together. They form a grid based on the following rules:
a) files are marked from left to right as 10-80
b) ranks are marked from White's side as 1-8
Combining these 2 together will give the proper designation for each square. Example 1.5254
This notation is best suited for correspondence chess since it enables players from all nations to transmit their moves in a totally unambiguous way, regardless of language differences.
Source: "International Correspondence Chess Federation"