"Where items overlap" and "What the totals include"
Two notes the grid puts above itself when its lines do not add up to its totals — and why that is right.
Where items overlap
A field marked several, or a field of a related entity reached through several records, puts a record under more than one item. Each line counts it; the total counts it once. So the lines add up to more than the total, and the grid says which field does this.
What the totals include
A calculated item is in every subtotal and grand total over its field, so those totals are more than the records' own. The grid names the item; an export says the same.