How to add

To find out the sum of a group of individual components, one must add up each of the components to arrive at the total quantity. This process covers both concrete and abstract objects (e.g., counting cars or counting thoughts).

When counting whole units (e.g., integers), and when using the base-10 numeral system, we find transition points after ten units (or multiples thereof) have been arrived at. What this means, in practical terms, is that if you desire to monitor an accurate count of an item, you will end up with whole groups (typically divisible by ten). One set of ten whole units is referred to as... ten. Ten units of tens is called one hundred. Ten units of hundreds is called one thousand, and so forth.

So, if I'm counting how many rounds of ammunition I've shot through one of my firearms, I consider one hundred rounds to have been achieved once I've actually shot 100 rounds through my gun. Similarly, I have not completed two thousand rounds of ammunition shot until I've actually completed shooting the 2000th round (note: do not make the mistake of thinking you've shot 2000 rounds upon completing shooting the 1999th round).

And, not surprisingly, the first set of ten individual units to be completed after completing the first 2000 units, does not occur upon completing the 2009th unit, but after the 2010th.