Personally, I use grams. More granular and easier to follow.
I use a spreadsheet in google docs where I plug in the weights each day that shows +/- that makes it really easy. Weigh the kitten, then plug it in on my phone. It also creates a graph and converts to ounces. A couple of other fosters use the same template, and there's the added bonus you can share the document with vets/medical staff.
#FosterPrograms