I'm a bit unclear on what you are asking so could you clarify? I've always determined the critical path(s) by network diagramming and calculating the total duration of each network path from start to finish.
My heuristic is that unless you have less than about a dozen events in your project plan, use software that automatically calculates the critical path, and that shows you where the problems are in your constraints. Saving Changes...
"This planet has - or rather had - a problem, which was this: most of the people living on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movements of small green pieces of paper, which is odd because on the whole it wasn't the small green pieces of paper that were unhappy."