Now it seems like a simple enough thing, the invention of or discovery of zero. And if you're me, where the sum of your bank account/groceries/life savings/investments/ is nil, then it's a logical enough extension to assign it a value. But really - think about it - that point where all quantities become equal - where you can compare all things - for zero apples is indeed equal to zero oranges, and think of how much our current number systems, computing, banking - depend upon the number zero, and maybe you'll realize that it's not such a small discovery. Or invention - (another post - are numbers and their inherent laws invented or discovered?). But as my mind certainly isn't up to fathoming the intricacies and nuances of such accounting, here are a few sites to lead your thinking on:
"Without the notion of zero, the descriptive and prescriptive modeling processes in commerce, astronomy, physics, chemistry, and industry would have been unthinkable."
Link: Wikipedia on the Number Zero
Link: Zero Saga