Hi Camille-Marie,
Can you show us your current formula and a screen shot of the table showing the column(s) involved in the calculation?
Double slick the cell containing the formula to open the editor.
Place the pointer just above and to the left of the circle at the intersection of the column and row reference tabs.
Press shift - command - 4
Drag the pointer down and right until the selection rectangle includes the columns that are highlighted in the colours seen in the formula, then release the mouse button to capture the image.
To include the image in your post here, click the 'two mountains' button (second last in the row of buttons below the message you are writing), then double-clck the image file ("Screen Shot " followed by the date and time). The image will appear in your post after a short pause.
More specific information will lead to a quicker answer.
Regards,
Barry