Okay, the user wants me to translate "difficult-to-measure" into Traditional Chinese. Let me think about the correct term here. The phrase "difficult-to-measure" can be translated as "難以測量" in Traditional Chinese. I should check if there's a more common or standard translation. Maybe "難測" is a shorter version, but the user might prefer the full phrase. Since the original is in English, I need to ensure accuracy. Also, the user specified to output only the translation without explanations, so I just need to provide "難以測量" as the result. No need for any additional text.