You are not the only one to get confused with volume ounces and weight ones.
When they printed DANDR in UK some "clever" editor realised that cup measurements are not often used over here for solid food so made the same error, so changed the allowed vegetable amounts of 3 cups to be some number of grams (don't have my copy here to find the number quoted) no matter what vegetables were chosen!

This meant lots of poor UK Atkineers trying to eat a pound or more of lettuce instead of 2-3 cups worth, which would be nearer to 4-6 ounces of it!!