>I would think a 2 sig-fig limit would be good practice >in FPLA rounding requirements.
The FPLA says that you 'should' use 2 sig-figs for quantities below 100 g. [begin quote] The SI metric quantity declaration should be shown in three digits except where the quantity is below 100 grams, milliliters, centimeters, square centimeters or cubic centimeters, where it can be shown in two figures. In either case, any final zero appearing to the right of a decimal point need not be shown. (Examples: "1 lb (453 g)" not "1 lb (453.592 g)"; "Net Wt. 2 oz (56 g)" or "Net Wt 2 oz (56.6 g)" not "Net Wt. 2 oz (56.69 g)".) [end quote] http://www.ftc.gov/os/statutes/fpla/part500.htm If you mandated 2 sig-figs above 100 g then you would need different labels for the EU and US. Whether that is important is another matter.
