I initially agreed with the take that Grace's ducktaped translation computer doesn't make sense, but we agree it's okay because we love Rocky enough to not care. However, I changed my mind and the way the computer works DOES actually work (arguably emotional inflections and variety of vocabulary aside). Rocky has a perfect memory; he doesn't need the computer to go both ways or his own database of english, because as soon as they establish what a concept is called in english once, he knows it. He understands Grace, he understands Mary, and he understands what the computer says he's saying. To Rocky, it's not a translator, it's an AAC device that Grace programs for him because he can't make human sounds himself. He uses words the computer knows, speaks the Eridian that he assigned to those words and asks for new words when needed.