A very important feature of Excel is its ability to trace and show the cells that are dependent on another, or which are precedent to it. These functionalities can be found on the Formulas tab; see the top-right of the image below:
For example, one could trace the dependent cells of the Price (cell C2) by selecting the cell and then pressing the Trace Precedents icon on the Formulas tab, giving:
The blue lines (s) joins the precedent cell (indicated with a blue dot) and the cells which are immediately dependent on it (indicated with an arrow); in this case, there is only one dependent i.e. cell C5, and hence only one line.
Similarly, one could trace the precedents of cell C5 by first selecting the cell and then clicking on the Trace Precedents icon, which would give the following:
Note that since there are two precedents, there are two blue lines which overlap. The blue dots indicate the immediate precedents.
These techniques are very important to follow and check the logic of models and the calculations.