An excel user should use a relative cell reference when it is important to preserve the relationship to the formula location. When you create a formula that references other cells, excel does not normally "record" the exact cell address. Instead, it looks at the at the relationship that cell has to the other cell containing the formula.
Based on the attached figure to this question, it shows that the split double arrow mouse pointer shows the result of moving the pointer of the mouse to the boundary between the column heading A and column heading B. (This answer is based on the actual options attached to this question.)
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