building a chain link fence?

[timber creek]

I'm going to be building a chain link fence. I got most of it figured out but how do you know how far to set the corner post so the link fits onto the bar that sides through the link. say I have 50' corner to corner well when you stretch it out hoe do you get the edge of the link to fit in the right spot to accept the bar that slides through it ? you know what I mean