| 1 | And just as each wave has a crest, it also has a trough. | |
| 2 | WITH luck, the global slump has reached its trough. | |
| 3 | The increase from trough to peak is minor: only around 25%. | |
| 4 | Its length shows how far she's gone, and the peaks and valleys reflect her speed. | |
| 5 | That, in turn, affects how the crests and troughs of the incident and reflected rays fall on each other. |