Okay, the user wants me to translate "sub-grade" into Hebrew. Let me check the rules again. The first rule says to translate all content into Hebrew. The second rule states that if the content is already in Hebrew, leave it as is. The third rule is to provide only the translation without any explanations.
So, "sub-grade" isn't in Hebrew, so I need to translate it. The word "sub-grade" can mean a subordinate grade or a lower grade. In Hebrew, the term for grade is "דרגה". The prefix "sub-" might translate to "תת-" which is a common prefix for "sub" in Hebrew. So combining them, "תת-דרגה" seems appropriate. I should make sure there's no existing Hebrew term that's more commonly used. Maybe check if "דרגה משנית" is used, but "תת-דרגה" is more direct. I'll go with that. No explanations, just the translation.