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Two tools, one refusal: nothing here compares floating-point approximations.

Compare fractions 5/8 vs 2/3 — settled by cross multiplication, shown on a number line. Compare measurements 5/16" vs 8 mm — both in both units, exact difference, which is larger.

Where this comes from. Exact rational arithmetic on the values shown — fractions are pairs of integers until display, and inch–metric conversion uses 25.4 mm to the inch, exact by definition since 1959. See the full methodology.