I bought it from The Sausage maker which suggests a teaspoon for 10 pounds, so if I use it I'll kind of use that as my sanity check. I usually do batches around 5 lbs. I figure what I measure out should be close to a half teaspoon, roughly, but I'll weight it out.
My current method with cure#1 is to cube up my meat, weigh it, then add my cure and spices and let it sit overnight to let the cure work. Then the next day I grind, mix, stuff. Then I either smoke it the next day or freeze the sausage to cook at a later date ( I tend to prefer smoking at barbecue temps just once). With the.sodium erythorbate you could just add the spices during mixing and you could stuff and smoke right away. Dunno if that necessarily makes a better or worse sausage. There's debate on it from what I can gather.
Also I don't think it has a concentration the way that sodium nitrite has Cure#1 does for instance, but I could be wrong.