I'm trying to calculate a value called, "additional throughput". It is calculated by subtracting the base case module's throughput from a new module's throughput.

In the sheet below you can see that for the third row down (has a blue box in it), that the additional throughput is calculated by the formula "=T6-T4".

The problem is that when I click on this box and drag it down to apply the same formula to the other rows, I want the formula to become "=T7-T4" for the next row. Instead it becomes "=T7-T5". I tried to select multiple cells (where the formula was manually entered) before dragging down so it could recognize that the T4 doesn't change, only the first part. However, that didn't work.

![Excel Sheet](https://i.stack.imgur.com/K79Pa.png)