Question

What is the uncertainty in the measurements allowed in the "Nutrition Facts" section on food?

Answer 1

Look on page 28 where fats are listed. In that same section you can see calories, how carbys are calculated etc. The uncertainty depends upon the amount; i.e., if less than 0.5 it will labeled s zero. Between 0.5 and 5 values are rounded to the nearest 0.5. Above 5 values are entered rounded to the nearest 1 gram.
https://www.fda.gov/files/food/published/Food-Labeling-Guide-%28PDF%29.pdf

The uncertainty is 0.5 g (for mass) from zero to 5 grams. Above 5 it is 1 g,