这个刚进大学的时候学过，后来忘了：）

You can calculate the standard deviation of the PRODUCT or QUOTIENT as follows:

(A ± a) * (B ± b) / (C ± c) = (D ± d) where * indicates multiplication (as in EXCEL)

A * B / C = D and d = D * sqrt ((a/A)2 + (b/B)2 + (c/C)2}

http://www.facstaff.bucknell.edu/kastner/CHEM221/announcements/sigfig.html