The entire set of activities in a project schedule is presumed to capture the entire contract work scope. The duration sum is an aggregated metric of the total number of work-days required to complete the entire contract scope of work. I cannot emphasize enough that each of the numbers from a single schedule by itself is not meaningful. It is not to be confused with contract duration, critical path, or longest path. But when you plot a collection of snapshots representing a baseline and periodic updates of the baseline, you see a powerful indicator. When you contrast the plotted Planned (Original) Duration Sum (PDS) line against the plotted Actual Duration Sum (ADS) line, you may be able to identify likely schedule analysis paths and more.
