do you know the rounding rules for the per 100g
Here's a good place to start. There are a lot of variables.
https://www.fda.gov/...Guide-(PDF).pdf
Below is an excerpt from page 130.
To express nutrient values to the nearest 1 g increment, for amounts falling exactly halfway between two whole numbers or
higher (e.g., 2.5 to 2.99g), round up (e.g., 3g). For amounts less than halfway between two whole numbers (e.g, 2.01g to
2.49g), round down (e.g., 2g).
When rounding % DV for nutrients other than vitamins and minerals, when the % DV values fall exactly halfway between
two whole numbers or higher (e.g., 2.5 to 2.99), the values round up (e.g., 3 %). For values less than halfway between two
whole numbers (e.g., 2.01 to 2.49), the values round down (e.g., 2%).
One thing to keep in mind is how much rounding can change the results.
You should use the raw data whenever possible.
Example (Using the values above)
Imagine you have your product tested and you find it contains 1.3g of fat in every tablespoon serving.
According to the FDA page I linked, you would round that down to 1g.
Now imagine you also want to include serving sizes of 1 cup (16 tablespoons) and 1 quart (64 tablespoons).
You might be tempted to use the rounded value to calculate these new serving sizes. (ex: 1g x 16T, 1g x 64T)
That would give you values of 16g of fat per cup and 64g of fat per quart.
The correct way to do it is use your raw data and only round at the end.
(ex: 1.3g x 16T, 1.3g x 64T)
This would give you results of 20.8g (21g) and 83.2g (83g).
It has the potential to make a huge difference. I hope this makes sense. Again, math is difficult to explain in text.
