Forty rods to the hogshead

Slashfood, on a quantitative definition of “gluten-free”:

Other countries including Canada, Brazil and Australia have defined gluten-free foods as containing no more than 0.0007 of an ounce of gluten for every 2.2 pounds of food.

Also known as “20 mg/kg.” Look, nutrition labels are already chock full of esoteric metric units like milligrams. Do we have to convert everything to “English” units? Are there readers out there who have a firm opinion on the appropriate gluten limit in ounces per 2.2 pounds of food, but who are unable to do the unit conversion themselves?

Or how about a compromise: Just say 0.002%, or 20 ppm.