How does the "Visits by Days Since Last Visit" calculate the visits?

How can I interpret the “new visits” and the “day 0” in this table? My first thought was that “day 0” is all of the visits in a current period and “new visits” is only the number of new visits (without the returning visits) in the same period but I double-checked it and I receive different visit numbers in the Overview menu for the same period so something is missing here. What can cause this difference?

The table can be found in the Visitors/Engagement menu.

Thank you very much for your help!