Recording the Association

Having formed associations, you will almost certainly want to know the events that contributed to them. One way to do this would be to capture the absolute time of both the primary and the secondary, as these times uniquely define the events. Another way to do it is to number events sequentially in the input file and record these numbers in the output n-tuple. This can be useful as PAW allows direct access to an event using this number. To make this easy TCA appends an extra variable, called ENTRY_NO, to the input n-tuple and fills it with this number. This explains what the lines:-

id_1         equals            entry_no_1;            
id_2         equals            entry_no_2;

do; they are recording the positions in the input file, of the events formed the association.