Does net margin correlate with growth of sales?

Studying one pan-Baltic enterprise, I came to the graphs of consolidated sales and net profit:

 

My somehow trained mathematician eye saw similarity between net profit graph and possible derivation of sales graph.

So, I derived sales graph, calculating "growth of sales" and plotted it against the net margin graph:

 

It looked pretty similar, I checked the correlation:

Yap!

Conclusions:

1) Sometimes textbook cases work also in real life;

2) In rapid growth environment expense growth is not catching gross income growth, net margin improves;

3) During slowdown we are bad and late in cost cutting and downsizing back to sustainable expense levels, net margin shrinks.