MT4 Strategy Tester passes - the numbers, what do they mean?

Can someone here help by explaining what the numbers mean when running optimisations in the strategy tester?

When I start an optimisation I see a series of numbers next to the upper left of the ‘progress bar’, like this:
‘16 / 10 496 (67 108 864)’

  • From experience I can see that 16 = current test pass
  • What is 10 496? It’s not always 10 496. This doesn’t get any bigger even if I throw more combinations into my EA, which I would expect. Also, the strategy tester sometimes stops short of completing this no. of passes.
  • What is (67 108 864) ?

…and to confuse things further, the Strategy tester has just completed 11 520 tests.

Many thanks
Paul