Reading a P6 Schedule Comparison Report, Line by Line

Sample Report: Six Rows, Four Kinds of Change

This is a fictional excerpt from comparing two updates of the same project -- the “before” and “after” columns are what each snapshot actually showed for that field.

A1040 — Excavation: Finish Date changed

A straightforward date shift, 10 days later. On its own this tells you a date moved, not why -- that requires checking whether this activity was actually driving the critical path, and if so, what changed upstream of it.

A1050 — Footings & Foundations: Total Float changed

Float dropping from 6 days to 0 means this activity became critical between the two updates -- one of the most important single facts a comparison report can surface, since it marks the moment an activity started actually controlling the finish date.

A1060 — Structural Steel Erection: Predecessor added

“Value not specified in the database” in the Before column means this activity genuinely had no predecessor at all in the earlier snapshot -- not a blank display, an empty field. The After column shows a real Finish-to-Start relationship now tying it to A1050. This is exactly the kind of gap the DCMA logic check flags on a single-schedule health check -- here it’s caught as a change between two schedules instead.

A1071 — Temp Shoring Removal: new activity

An activity with no row at all in the earlier snapshot. Added activities deserve scrutiny in a delay dispute -- scope genuinely growing is different from work that was always planned but only just got added to the schedule.

A1080 — MEP Rough-In: Lag changed

A relationship that had zero lag now carries 5 days. Lag changes are easy to miss reading a schedule casually, since the activity’s own dates might not move at all if it still has float to absorb the new lag -- the report catches it because it’s comparing the relationship itself, not just resulting dates.

A1090 — Interior Framing: unchanged

Included specifically to show it wasn’t touched -- confirming an activity’s logic and dates held steady can matter just as much as flagging the ones that moved.

Why This Format Is Hard to Work With at Scale

Six rows read easily. A real comparison between two updates of a 2,000-activity schedule can produce hundreds of rows in this exact same dense, text-only shape -- readable line by line, but hard to see patterns in: which changes cluster around a single disputed period, or which activities moved onto the critical path together as a group.

Frequently Asked Questions

What does 'value not specified in the database' actually mean?

It means the field was genuinely empty in that snapshot -- not zero, not an error, just no relationship (or date, or resource) existing yet in the schedule's underlying database at that point. It shows up most often on a relationship field for an activity that hadn't been logic-tied into the network yet.

How is a relationship change reported when the relationship TYPE changes, not just the predecessor?

A well-built comparison reports a Finish-to-Start relationship becoming Start-to-Start as a single 'relationship type changed' event on that one link, not as a delete-and-re-add of two separate relationships -- the distinction matters because a delete-plus-add can misleadingly suggest the logic tie was broken and rebuilt, when really the same link just changed type.

Why do some rows show no change at all?

A comparison report typically includes every activity present in both snapshots for context, even ones with zero differences -- seeing what stayed the same is often as informative as seeing what changed, especially for confirming that a disputed activity's logic was genuinely untouched.