It is confusing, but I do not think the amounts of yeast given here are correct. To convert by weight: Dry yeast to fresh yeast, divide by 4, then multiply by 10. Fresh yeast to dry yeast: Multiply by 0.4. Therefore, 3/4 oz dry yeast equals 1.875 oz fresh yeast, and 1 oz fresh yeast equals 4/10 oz, or 2/5 oz dry yeast.
Wonderful Jamie Oliver recipe!