Let's configure the pointer. Select the gauge pointer, then right-click on it. From its context menu, select Pointer Properties:

Set its value to [SUM(SalesYTD)].

Let's add another pointer. Select and right-click on the gauge itself, select Add Pointer from the context menu to add a secondary pointer. Set the value of the second pointer to [SUM(SalesLastYear)].

Change the color of our primary pointer, fill color to lime green and the secondary orange. What we want to achieve by the two pointers on the same gauge is compare the current sales with the previous sales value at the same point in time.