The sample recipe states 90ml of butter, last time I checked it was solid. I have no idea how you would work that out. Wiki says it’s 911g/l so I guess you use about 80g which is easy enough to measure, but why not list the weight (for cooking on Earth weight and mass are interchangeable)

I’m not sure why it’s talking about “cups”, I thought americans used “gallons” or “fluid ounces” for volume? It also has one ingredient that has accuracy to 3sf in its weight (167 grams) which seems rather excessive for cooking.

In theory you can use volume to measure things like flour, although it is trickier than using weight as you have to smooth it over.