When you’re trying to work out exactly what is behind your P&L figures (or any figure), you can read the formulas, and when you’re editing a cell, Excel has the good sense to highlight the precedent cells (the cells referred to in the selected cell).
Except when the spreadsheet is so complex that all the precedent cells are not visible in the same window. They could be anywhere. And then you have to go and find them. And you lose the other cells. And the source formula.
Use Formula > Trace Precedents. Excel will draw some nice (persistent) arrows for you, from the selected cell to its precedents.
Or its dependents (the cells which depend on the cell you’re looking at) even!
And you can even select Trace Precedents or Trace Dependents again, to have arrows pointing at the precedents of the precedents for your cell.
When you have covered your spreadsheet with little blue arrows, you can Remove Arrows to clear the air.
If you haven't already, give it a try. We're sure you'll love it.
You can even take it up a notch with some shortcuts: