Citation, Documentation of Sources

Q. From a Spanish-speaking company I have many financial documents containing large numbers (billions, trillions). As I understand it, the best practice is either to leave the complete number as is or to round it (1,256,128,023 or 1.3 billion). Is there a rule regarding how many places after the decimal point should be shown? My client wants as much information as possible to be communicated, but it seems to me that, in English, we rarely see anything beyond one place behind the decimal point.

A. It’s a matter of judgment, although as you say, one decimal place is conventional. If your client wants as much information as possible, it would be best not to round the numbers. If you can, ask the client to state a preference. Take care, too, when translating terms like billion that may look the same in both languages but actually express different numbers (see CMOS 5.250, s.v. billion; trillion).