Wolfgang Schaeuble was playing Sudoku on his iPad as he waited to hear whether Greece's negotiating team had persuaded private creditors to accept a bigger loss on their Greek bonds.
Germany's finance minister needed this last piece of the debt restructuring puzzle to fall into place.
Without the private creditors - banks, insurers and investment funds - a 130 billion euro (109.7 billion pound) deal to save Greece from default could fall apart. The consequences for the euro area would be catastrophic.
Schaeuble finally got what he wanted only hours before dawn on February 21 after negotiations that ran all night.
What emerged was the world's biggest debt restructuring deal, affecting some 206 billion euros of Greek government bonds, according to law firm Linklaters which acted as adviser.