A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
That is not possible - with icon sets, you cannot use relative references to other cells.
You can do the following, however:
In B2, enter the formula =A2-A1.
Fill down to B7.
With B2:B7 selected, click Conditional Formatting > New Rule... on the Home tab of the ribbon.
Select Icon Sets from the Format Style dropdown.
Select the red, yellow and green arrow (the top item) from the Icon Style dropdown.
Select Number from both Type dropdowns on the right hand side.
Excel will automatically enter 0 in both Value boxes. Leave it that way.
Select > from the dropdown to the left of the first Value box.
Tick the check box "Show Icon Only".
Click OK.