- Total counts every event.
- Unique counts distinct visitors per day. We recognise a repeat visitor on the same day from a hashed combination of their network address and device details; the hash key changes every 24 hours and the old key is destroyed, so the same person on two different days counts as two uniques. We do this on purpose so that we never store addresses that identify people (see our Privacy Policy).
So "unique visitors over 30 days" means "the sum of daily uniques", which is slightly higher than a true 30-day unique count. For campaign comparisons this is consistent across all your links.