Here's my calculations:
According to the book,
METRIC yeast = 75g fresh; IDY equivalent = 25g
HOME yeast = .09 oz, x 28.35 to get grams = 2.55 g
The HOME formula, based on total weight, is .32 of the Metric formula, so 25g x .32 = 8g IDY.
Yep, that's off too.
So let's go with the percentages column instead.
Metric: Flour = 1500 g
Fresh Yeast = 75 g, which is 5% as noted.
Home flour = 17.6 oz = 498g
so 5% of that should be 25g fresh. We need to divide by 3 to get IDY = 8g
.09 oz = 2.5g, this is a ways off the expected 8 grams.
Yup, I think we have another error.
I think that basically, the yeast in IDY form, needs to be 1.6% of the flour weight (5% fresh divided by 3) so 498 x .016 = 7.96g which is .28 oz - let's call it .3 - which is 2.7 tsp according to page 388.
Anyone else what to have a go at the math here and see how close we are?