AlpineQuest & OfflineMaps

If I tap a displayed map layer, I see an item called "Compare..."

In it there is checkboxes. (Including one oddly for the same map as I tapped.)

But on https://www.alpinequest.net/en/help/v2/maps I can't find any instructions about what this is supposed to compare.

Check the maps you want to compare, then OK.
You'll be able to display them sequentially.