Attach a source note to each food-label quantity you share
A source note should identify the exact observation, package version, location and date that support a comparison.
A link beneath a comparison is useful only when a reader can tell which statement it supports. Attach each product-specific quantity to a particular package observation or matching source section. A general nutrition article cannot verify the amount printed on an individual food.
Separate rule sources from product sources
The FDA guide to reading nutrition labels explains how serving information and nutrient quantities relate. It can support your interpretation method. It does not establish that a named snack contains the amount you entered into a calculator.
For that amount, use the readable package image or a clearly matched product source. State which one you used. If the quantity was transcribed from your own photograph, give the photograph a stable reference and retain the product identity beside it.
Write a reproducible source line
A compact source note includes product and variant, market, source type, specific panel or section, and observation date. For a webpage, add its exact URL and any displayed revision date. If no revision date is shown, do not invent one from the date you visited.
A fictional example might read: sample cracker A, plain, 150 g, US package photograph A-back, sodium row, 120 mg per 30 g, observed on the recorded date. The derived result is 400 mg per 100 g. Keep that calculation in a separate sentence rather than implying the package printed the derived figure.
Show evidence gaps directly
If the source image has an unreadable serving heading, identify that gap. A link to the product's homepage does not repair it unless the matching page actually provides the missing information. Similarly, a source about sodium generally does not verify a specific product's sodium value.
When sharing a comparison table, place the source reference in the same row as its product. That layout reduces the chance that a reader assumes one citation covers every entry. Preserve the original source wording where a quantity uses a qualifier such as less than.
Review the source note whenever you update the result. If you replace the product version, update the evidence reference and observation date too, while keeping the earlier comparison archived with its old source. A well-matched citation tells the reader not just where to click, but what they should be able to verify there.