Every change to a baseline creates a new baseline version: adding or removing items, and re-pinning an item to another item version. The comparison shows what differs between two of those versions, so you can answer "what changed in this baseline since the design review?" without reading through every item.
Opening the comparison
There are two ways in:
In the baselines list, or in the Baselines tree in the sidebar, click a baseline's ... button and choose Compare. The comparison opens with the current version on both sides; pick the versions you want in the dropdowns.
Open the baseline, click Baseline settings, then the clock icon to open the History tab. Click any earlier version in the timeline to compare it with the current one. The step labeled current is the version you are looking at; latest is the newest one.
Choosing the two sides
The Baseline comparison window has a version dropdown for each side. Each entry reads Version n, marked (current) or (latest) where it applies, followed by the date that version was created. The left side is the older state, the right side the newer one; you can pick any two versions, including the same one on both sides.
Item view
The Item view tab lists every item that appears in either version, one row per item, with the left and right pinned versions side by side. A mark next to the ID tells you what happened:
+ (green) - the item was added; it exists only on the right.
- (red) - the item was removed; it exists only on the left. Removed items are listed at the end.
Dot (purple) - the item is in both versions but pinned at different item versions.
No mark - the item is pinned at the same version on both sides.
Gray dot with Item is restricted - the item is in the baseline but you do not have access to it.
Each side shows the item's short ID, title and a version badge. Items that were deleted from the live project carry a deleted tag.
Tree view
The Tree view tab shows the two versions as flat item lists next to each other, in the order the items were pinned. Hover an item to preview its content at that version. Use this tab to eyeball the overall size and order of the two sides; use Item view for the change status.
Going deeper on one item
To see what changed inside an item, open the baseline, click the item's version header and use Compare with current baseline version on an older version. That opens the field-by-field diff of the two item versions.