Hyphens, En Dashes, Em Dashes

Q. I have a question about physical quantities in a sentence: “Berry (1979) did more tests on the 2-gram tablets.” Is the hyphen correct?

A. Chicago style is the same for all physical quantities. Please see our hyphenation table (section 1, under “number + noun”). In nontechnical text, we spell out the number (a two-gram tablet); in technical contexts, we abbreviate the measure and omit the hyphen (a 2 g tablet).