Unique Visitors on the Tagalys dashboard are calculated based on unique device IDs. A user visiting your website multiple times from the same device will be considered as only 1 unique visitor. Click here to learn more about 'Unique Visitors' on the Tagalys Dashboard.
However, the above value is not the case with the Unique Visitors count in the downloaded reports. In the reports, the Unique Visitor count is feature-specific (Collection, Search, Recommendations) i.e, every time a visitor lands on a collection page or clicks on a recommendation widget, they are regarded as a unique visitor.
For example, when user A visits two collections, Collection A followed by Collection B (via the same device), they are considered a Unique Visitor to both collections in the report, and this is reflected once the report is downloaded. However, to avoid the visitor being counted twice, the unique visitor is attributed only to Collection A on the dashboard.