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Autofill is a feature that enables you to copy the contents of a cell to another cell or even a range of cells within the grid.
Autofill in all directions
Using the tiny square small square in the corner of the selected cell, known as the 'fill handle' in the corner of the selected cell, you can drag it (drag-move it down) to repeat the values from the cell.
Double-click the fill handle in cell B4 where the value is 30 to , to fill the selection down to the last value in neighboring column, just like it would in Excel or Google Sheets.
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