[thaumasiotes]

"We use commas to divide large integers into groups of 3 digits. Grouping is done from the right end of the number, for example: 17,000,120".

Those two rules are, to my knowledge, the entirety of the US number-commaing system. How did you spend an hour on it? It might be difficult for people to understand it before having it explained, but I wouldn't call it complex.

[downandout]

She just couldn't wrap her head around it. Kept going back and forth. She was trying to determine whether a number in a document she was translating meant million or billion.