Unless you know it and it is a specific one. Because everyone’s calligraphy is good or bad, some are valuable or not valuable, some are expensive and some are relatively cheap, so we cannot generally use square feet to talk about it, we can only say how much a certain calligraphy costs per square foot. Runge doesn't have any accuracy, it's just a reference. It mainly depends on his own judgment and understanding of his calligraphy and painting, as well as the market hype at the time. It’s my own opinion, please forgive me if I’m wrong!