321 PRODUCTIVITY and 'Double-Sixteen' WHY do so many darts-players, getting down to a double, prefer to leave themselves 'double-16'? It's because they believe in productivity (though they certainly don't think of it that way). Here's why it's so: with double-16, getting a single 16 leaves another double to go at straight away. And so on, right down to double-1 (though let's hope you don't often have to go that far). You don't need to waste time in "knocking off the odd". In other words, you've planned the job to go as smoothly as possible.