Labelling
Three percentage points, not three percent. A label saying 40 is satisfied by 37, and that is not the same band.
— pp
Negative means a fibre is outside the band
The tolerance is applied as percentage points of the total fibre weight, which is what 16 CFR 303.43(a) provides and what its own worked example shows: a declaration of 40 percent is satisfied anywhere from 37 to 43. A deviation of exactly the tolerance is inside it, because the section speaks of a deviation in excess of the figure. Where a label represents the product as composed wholly of one fibre, paragraph (c) withdraws the tolerance, so this tool applies a band of zero the moment any declared figure reaches 100 - a result of 99.2 against a claim of 100 is outside a band with no width, and reporting it as a deviation of 0.8 against a tolerance of 3 would be the wrong answer twice over. The tolerance field is an input because three percentage points is one jurisdiction's figure, read here from the section itself; a reader working to another market's rule enters that rule's number. Nothing here decides whether a product is misbranded: paragraph (b) leaves that turning on whether the whole deviation arose from unavoidable variation in manufacture despite the exercise of due care, which is a question about a mill and not about arithmetic. Declared and found totals are shown because a test result that does not sum to one hundred is a reason to look at the test before looking at the tolerance.
Fibre Content Label: Declared Blend, Test Result & Tolerance — free, with the formula and a worked example, at Textile School.